All my notes take the form of questions and answers now. I find that notes that can't be used to challenge me to recall and think about the material are pointless.

Note these are not like SR flashcards, which I have had little luck with outside things such as vocab.

I keep them in markdown in Dropbox, and edit them on my iPad or phone while reading. When I feel like reviewing I have a custom style sheet to present them in a form that it is easy to cover up the answers with one hand.

In terms of deciding what information to capture, I used to fetishise names and dates and things. Nowadays I focus mainly on concepts (if the author names the concept it's gold) and the outlines of arguments, and try to keep the volume to only the most important info, since everything I put in there I expect to remember.