1. I take a lot of notes because my working memory is shot to pieces. These notes are often unintelligible after even a short amount of time. These kind of notes are ephemera.
2. I take notes and I consolidate notes. Consolidation is what turns my notes into something worth keeping or discarding. More important things get more consideration which translates to more editing which results in more coherent notes. These are notes that are more likely to be typed up (a good example of that is my reference sheet for my financial information and accounts. Nobody wants to try to remember account numbers or the like. This is currently a simple open office document. Nothing fancy).
   
   I want there to be a good filing/structural solution for notes but I find that largely gets in the way because there's no clear paradigm to follow. Most of my stuff ends up in a commonplace book format for that reason.
3. A good example of non-note note taking for me is pintrest. Note taking software is notoriously horrible at dealing with media. It doesn't have any good reason for being terrible at that, and it seems like a logical point of competition with paper solutions.
4. Scans go straight from my android phone's camera to my google drive or google photos, depending on use case.
   
   I will email notes to myself if I have to but I've deprecated that method.
   
   Every single wiki/note/knowledge management system you can think of I've used or still use. OneNote is a current dumping ground, notion if I can be bothered cleaning up the notes.
   
   My quick typed notes on PC are usually done in Notepad++. This is another one of those it just works solutions.
   
   I am basically paperless, which is something I didn't think would happen. That being said, having the devices to do it and having an ideal process are two very different things.
   
   I have my (android) phone which I can use to access data. A phone is a bad device for anything but photos/scanning and reading notes, editing is too much of a pain. Lots of problems that should be solved aren't solved (interoperability is a sore point everywhere), and for no good reason that I can see other than nobody has bothered to address it.
   
   Tip: sharing something to google tasks is a very quick and easy way to sync data between android and pc without any grief. It just works.
   
   I use a Boox Note, which is an android tablet with an e-ink screen and a wacom digitiser. Aftermarket Staedtler Norris digital stylus. Only the built in notetaking app supports fast refresh, and that's what you need for notetaking to work on e-ink. The api to implement fast refresh exists, as far as I know nobody has ever used it on public software. This device is a solid note taking experience. E-ink draws next to no current so the uptime is weeks. Syncing is mostly a non-issue (all these things have their own quirks. Provided you want to do things the way the vendors want you'll have no issues. I never seem to want to do things the way vendors do, so I always end up in the weeds at some point). This was my primary note taking device for several years, and I still use it depending on the situation.
   
   I recently bought an iPad Air for the drawing and note taking (mainly because I wanted colour and you can't get that with e-ink yet). The iOS ecosystem and I do not see eye to eye all the time, neither do I with various software within that ecosystem. Interoperability between ios, android, and pc can be annoying. The apple pencil isn't perfect but it is way better than most vendor offerings you typically get. I don't know how I feel about the optional handwriting input at the system level. Yes it works but it has some quirks. The pencil can also be a bit twitchy with double tap switching. Note taking software is a sticking point at present. Notes are mostly in GoodNotes, separated into books (which is pretty much the same as what I'm used to on the Boox). Apple notes is more of a scanner IMO. I want to love Concepts but I hate it - the idea is sound but the drawing and writing feel is all wrong. Syncing for all software is garbage (which is part of the interop issues).
   
   Tip: custom templates for note taking software will make your life better. In the past I've made paper forms that I've printed out to use back when that was difficult to do on pc. Making the digital equivalent of a custom form for capturing certain types of data is every bit as useful. A good example of that on my current devices are fashion design bodyforms - you don't care about the pose and you don't want to waste time on a task that never changes. Note taking is a data collection issue, optimise for whatever you collect a lot of.
   
   I am constantly looking for my Holy Grail of software that will magically solve all my note taking problems. I am always teetering on the edge of actually programming my own software, more out of the spirit of Fine then! I'll do it myself! than any sort of actual interest in the area. Digital should be more than paper (because we already have paper) and there are a number of obvious (eg. why can't I treat my ios or android as a printer from other devices? It is a display device) and less obvious ways (eg. if a device can perform OCR in real time and predictive text is a solved problem then why can't we have handwriting completion? Macro expansion would be even easier than that) that digital could easily have more value than simply aping paper.
5. My working memory is garbage, so that's the first use case. If I can't see things, they don't exist. If I don't write things down then they'll probably be forgotten within minutes. Notes are a way to be able to pause and resume tasks that my brain can't do anymore.
   
   Consolidating notes is part of understanding the material. It's basically explaining it to myself in the future. I find this to be particularly useful when it comes to obscure tech support issues. Plenty of things in that realm make you think I never want to do that again and then document it so you don't have to.
   
   It's all reference material, it's all about outboarding memory and creating external indices. The day I can get a production ready neuroprosthetic hippocampus that outperforms what I have to hand then all my note taking is going into the garbage.
   
   I have no evidence for it but I think that handwriting may have particular effects on learning and retention that typing might not.

I prefer to takes notes on paper. All the time. Paper is immediate and always on. "But it is not digital!" they say. Doesn't matter. I don't use it like persistent memory - "disk" - but more like a RAM expansion for my brain. I have so bad - albeit fast - handwriting that I need to process it quickly anyway. And my process calls for that: I convert the notes into actionable and tangible outcomes quickly - and these are usually digital:

• follow-up messages to other people
• calendar invites
• updates to documents/wiki pages
• todo-list entries/tickets 
• Anki cards

The latter is my way of ensuring long-term retention of new, relevant, or interesting concepts. I do not use Anki for memorizing facts but reminding me of concepts/habits/practices.

My favorite note-taking software is CherryTree, but at work I use OneNote if installing new software is against company policy. Ultimately what I want is pages of plain text which are organized in a tree structure.

As a part of my work I make notes regularly. Each new task gets a new page: it starts with a link to Jira and a copy of task description; followed with all task-related facts I found, questions I want to ask/explore, etc. The purpose of this is to be able to continue if I get interrupted or on the next day, because my memory sucks. Sometimes I use writing as a form of rubber duck debugging. After finishing the task, the page is moved into a "completed" folder (sometimes organized by year and month) and typically not edited anymore. As a side effect, it allows me to provide an occassional summary when someone asks what I have been working on this year.

In addition to that, I also have a topic-oriented hierarchy. The top nodes are "company" for information about company in general (processes, colleagues...). A top node for each project I am working on (data model, API...). The last top node is "knowledge" (useful pieces of information about programming languages, frameworks, and tools). This information is updated when I learn something that seems useful, and referred to when I need to remember something I know I made a note for. I do not aim to have a complete documentation of something (that would take too much time) but rather to cache everything that I already spent time to find out.

(Sometimes my colleagues object when they see me making private notes. Like, why don't I update the company wiki instead? The answer is that my private notes are allowed to be idiosyncratic, incomplete, low-status; and I am free to use the most convenient tool for the job. Writing for others using tools selected by others is more than trivial inconvenience -- waiting a few seconds after clicking each button, fighting with the formatting... That said, yes, I also contribute information to the company wiki once in a while.)

At home, the top nodes in my hierarchy are "to do / planning / projects", "finance", "various know-how", "mathematics", "computer science", "programming", "useful software", "games", "books", "internet"...

I am using this kind of system for several years. Previously I tried to develop my own software (Notilo) optimized for my personal quirks, but it was quite lame, and when I had kids it became impossible to maintain it, so I switched to CherryTree. Unfortunately, I have a lot of notes in the old format, which I hope to convert (probably by manual copy-pasting individual pages) one day.

What role does note-taking play for you? Is it a way to focus your attention? To make extracts from the text for easier reference later? To comprehend the material better through the act of making notes?

All of the above, with different parts of the system optimized for different purposes. Generally, there is a "diary" part and a "reference" part; the former helps me focus on something at short term and sometimes serves as a log in long term, the latter allows finding things easily later.

The particular technology stack I use for notes on reading is {Instapaper, PDF Expert on iPad} -> Readwise -> Roam Research -> Summarize it.

To answer your specific questions:

1. If I plan on summarizing, I tend to only highlight important bits. I write down any connections I make with other concepts. Readwise reminds me of 15 highlights I've taken in the past per day, which I've been doing for about half a year. I'm not sure if it's helpful, but the time cost is low, so I continue.

2. Sometimes if I want to know what I thought about specific posts. If it's just high-level concepts, I'll generally just skim the relevant material. If I find myself looking something up more than twice, I'll put it into anki.

3. No, but I only really study technical things. I find it difficult to summarize/remember history, plausibly because I don't change the way I take notes.

4. Roam Research seems pretty good. RemNote is similar and incorporates more spaced repetition. SuperMemo allows one to create flashcards as they read (readwise does something similar, but the functionality is worse, I think [I've never used SuperMemo, but plan to try it]).

5. Attention, future reference, and comprehension are all goals. The primary goal seems to be forcing connections with other ideas and forcing myself to have an opinion about what I'm reading at all.

1. Almost never when learning a new skill etc. Commands, sometimes, but the setup cost is way too high.
2. Often. Especially for things like plans etc.
3. I keep a journal whenever I remember to do so. Planning or things I need to do when working towards certain goals are worked out on a whiteboard for the outline, and then filled in with more and more details.
4. I used a bullet journal for a year or so, and a physical journal for a year. Keep for a while in the past, then OrgMode, and now I'm using Obsidian.
5. To not forget my ideas. I have too many. Most still end up forgotten because I didn't bother to write them down, but still.

1. Not very, still developing habit.
2. Mostly for work-related minutae, but trying to expand that.
3. Yes. I keep a stack of clipped together A8 sheets of paper on me at all times (essentially as a "RAM" extension), write a (modified) Bullet Journal, and keep an Obsidian vault with more topic-oriented permanent notes (this is also where book summaries go). I also use Zotero for digital collection management.
4. Sort of. I've tried a few different ideas (Zettelkasten, Bullet Journal, Getting Things Done, Cornell notes, plus some hacked-together monstruosities) for several months at a time. So far nothing stuck for more than a year.
5. I find it that the problem with memory tends to be retrieving memories, rather than storing them. I.e.: things are in my head, I just... forget that is the case. The exception is permanent topic notes. I write these longform for six-months-in-the-future me.

When I was young (high school, uni), then didnt really bother. I had excellent memory for anything that engaged me. I would note on paper things to look further into because I didnt immediately understand or wanted to further reference (still do this) but not much else. With textbooks, it would be turn straight to problems section and work backwards. This approach did not age well. 

I heard about MindMap methods at a DEC user group conference and I started using those. I found drawing them was an excellent way to get stuff into my memory but that I seldom referenced them. (Seldom kept them even). Best of all though, the practice of using them helped me notice what was important to note (as it triggered other memories etc). 

 Memory now isn't what it used to be and I find notes very important. Writing on paper seems to be good for committing to memory but terrible for retrieval (cant remember where I put that piece of paper.  :-)  and my handwriting is terrible and getting worse). For quite a while, I used a hardback note book and put everything in it. I now transfer smartly to Google Keep as can search easily and it is available on phone or main computer. What is actually on those notes though is pretty cryptic to put it mildly. I stick to noting the "nodes" that I would use in mindmap. So far works well enough (started using Keep in earnest 5 years ago) but we will see how it goes as age  continues to degrade memory.

I like using a wiki for notes. Something like this: http://evergreennotes.com/. There are a lot of ways to set up a wiki.
 

1) How consistently do you take notes when you're reading up on a new skill or subject?

I take notes for things that I want to eventually write something about, so for most things I don't end up taking notes.
 

2) Do you regularly refer back to old notes?

Sure. Especially keeping track of relevant sources is super useful for future me.
 

3) Do you approach note-taking differently for different subjects or purposes?

For notes that I don't want people to see because they involve private information, I just use a repository with some files and folders on my computer. For anything that I'd be ok with people reading, I use this wiki: openquestions.wiki.

4) Have you adopted a specific note-taking method and used it consistently for more than a few months?

Yep.

I'm not sure if the method has a name. For my personal notes I have a folder for free form babble type thoughts. Each filename is just the date that I'm writing. Then I later go through and find anything related to some topic I want to do more work on and copy past the good bits into files separated by topic.

Some of those notes in my private repo end up being something I'd like to share with friends, so I post 'em to my wiki.

5) What role does note-taking play for you? Is it a way to focus your attention? To make extracts from the text for easier reference later? To comprehend the material better through the act of making notes?

The free form writing helps me to get down my thoughts quickly for possible future reference. Sometimes I go back to what I wrote 5 months ago and find some gems.

Sometimes when I'm researching a topic, just copy pasting links and relevant text has been useful.

Taking notes helps me keep track of fragmentary ideas for future processing and helps me do the processing.

My current note taking art is abysmal. In order for notes to be of use, I think they need to be timely, and refer to your current goals. My life is too transient at this point to really benefit from note taking. 

In the past it was honestly the most important thing I did in terms of organizing my thinking, my time, and my effort - especially my thinking about all of those things and how they related back to me. 

I had worked at initially using a single notebook to act as sketchbook, journal, planner and organizer. I developed a system of notation and indexing to be able to reliably refer back to important info, ideas, or sketches. But as my ideas grew, I found I needed to start keeping my journal separate from my sketchbook and from my ideas book, so I developed an organizing system for the different books and worked at attempting to create basically a paper filing system I though of as a paper based database.

It allowed me to study information hierarchy, and learn all kinds of different things about data structures and the meta structures needed to make them easily retrievable and to be able to integrate them. 

I even tried my hand at attempting to encrypt them, to make it difficult for anyone who might get access to them to be able to make a lot of use of the information. My last relationship ended badly, and while I can't prove anything personal or creative content was leaked, in my less generous moments I wonder.

But currently, it's all sitting in a couple of boxes in the living room under some dust cloths, but I was unable to keep up with it for 4 years, only just recently got it back, and while I leaf through them once in awhile, I pretty much just imagine what could have been. There are still some good ideas, but I'm not in a position to do anything with them right now, so there's no real reason to take notes like that right now. 

Bullet Journaling - I got into it several months before it became a big thing all over Youtube several years back.