I keep it in a flat text file. It's maybe three or four screens long.
Now, for that to work, I obviously don't store "the knowledge gained in a day".
Some things I learned I'm going to use all the time. I don't worry about them; I'll use them often enough that I remember.
Some things I learned are interesting in a "huh, interesting" kind of way - mild surprise, and then move on. I don't bother with them, either, because who cares? They aren't worth remembering.
Some things change who I am. I don't bother writing those down, either. They are recorded in who I am; I don't need a file of notes. (They might be interesting to someone else, but so far the world is not beating a path to my door to read such a file.)
Some I can just Google. I can search Google as fast as I can search my notes file - faster, because I have Google on more machines.
The only ones I bother to write down were ones that took some digging to find out, and that I'm probably going to want to know how to do again, but only rarely. That is a small number of things.