This is not my work. Sharing as it has huge amount of information about the game
Hentai_High_School_-_JPS_Full_Guide.txt
https://f95zone.to/threads/hentai-high-school-v1-10-1-2-hhs.1016/post-1036127
Mild warning that (assuming the link is the correct source) that guide's from 2018 (and mentions 1.9.5 inside), so may out-of-date for various quests or systems that've been reworked since. For example, starting the lock-picking system is no longer simply "buy a lockpick".
I had been thinking about trying to write-up something kind of event guide like this, since I play with VSE open anyway, documenting would be as-fast as hunting down the right event every time. Maybe next play-through.