I have no idea; but it may help to ask yourself what you would be doing if you already had it - a list of that last 20 surprises.
For example you might try to better prepare yourself for something. i.e. find a way to make the surprising situation less surprising.
I read the article found at:
http://www.fastcompany.com/3035671/how-i-get-it-done/a-new-technique-for-creating-more-aha-moments-the-surprise-journal
I started writing a few things down. I realize that the point of the surprise journal is to give your brain a little reward for noticing something. So, the actual keeping of the journal is surplus. You could write it down and then throw it away.
But that feels intuitively like an open loop. Is anyone doing anything with a surprise journal after writing it down?