I have no clue when a girl orgasms or not. Unless she tells me, your guess is as good as mine. I know there are some signs like a sudden change in vocalization (e.g. “I’m coming”) or a request for a one-minute break, but it’s impossible to be certain unless I ask. And while I’m curious how many multiple orgasms I did or did not give in a 30-minute period, I don’t ask.
If I ask, I’ll start focusing on her pleasure instead of doing my own thing, which — if I hear from her again — is good enough. The moment I try to please her is the moment I’ll end up pleasing both of us less.
P.S. I have not gone down on a woman since 2003.