Still talking about SumireTeru, right?
Abnormal experience is kind of an odd bird. You generally get a point or two in it the first time you do something, well, abnormal. So it's almost like an achievement system rather than the usual "how many times in her butt" or whatever like other kinds of experience. It still just counts up from zero, though, although some flag somewhere has to be set in order for the game to know what kinds of abnormal experiences you've already had. So that one might be hard figure out from the game files.
I know for certain in SumireTeru that getting her to insert Mahjong tiles anally is one way to get one or two Abnormal XP. I also am pretty sure that gaining Abnormal XP is a quick way to get her to try suicide if you haven't gotten her past... uh, some point in affection or lewdness. I don't remember which.
In other Era games, Abnormal XP comes from things like urination, bestiality, public or on-film masturbation, ass-to-mouth, incest, losing virginity to a sex toy, losing virginity to a futa, being turned into a futa or having gender changed, very large ejaculations or lactation... but that's like three other games' worth of examples. I kinda stopped playing SumireTeru, so I'm a little rusty on which of those might count as abnormal XP in it.
The guys on 8chan have a thread archive at the top of their eragames thread. I remember a lot of discussion a few months ago about abnormal XP in that game. You could try looking through their thread archive for more details, although when I did a few minutes of checking it seemed mostly to have archived threads from a year ago. Maybe they're just not in order.
EDIT: Okay, did a kind of half-assed source dive. Here ought to be a list of everything that can get you Abnormal XP. I assume these are all only awarded the first time you do them. The stuff with the (?) is stuff that I don't think I've personally seen in the game or otherwise suspect might not be implemented.
There's a lot of "I guess" in there because I literally just searched for the words "abnormal experience" being printed without going through all the labor of checking to see that those are actually reachable, etc. That'd be kind of a bit more work than I want to handle right now.
Anyhow, good luck.