You should note which domains make you surprised frequently, and consider explicitly revisiting your models and assumptions in that domain.
You should notice which domains don't have great models, and check that you are surprised there as frequently as you'd expect - or note that you fail to be surprised, or that you treat everything as equally likely in those domains, and consider if you're doing well.
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.
There are different ways to notice 'things'. Surprise is only one trigger. Going through the world with open eyes.
I notice when my children do something they didn't before. I keep a child development diary where I collect what I notice about them. Noticing alone is surely valueable because it is accompanied by a warm feeling of parental proud. But it is also helpful when reading it later - e.g. when the next child reaches that age. It allows to put observations in perspective. Yes indeed this reduces the surpris of some of these later. But that is also a satisfactory feeling - to notice correlation.
Other people may notice different things. A physicist (or like minded) might notice how pieces move in the soup. Or how much wind leafing through a book causes. Or how knots seem to form automatically in cables and strings. Or how sometimes clothes collect in the sheet in the washing machine. Someone else notices how decisions are made by some groups and how it fails for others. How long it takes for decisions to settle. How variable participation is or how it feels to not being part of a decision.
Is this surprise? Is this curiosity about reality? Do some people have this more than others? Can such a mindset be acquired?
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?