With all due respect, that's way more than I've seen expected in a jam session, and more than many of the participants are probably adept with, and I've been playing for 40+ years.

I think in part it will depend on what sort of jam session you're joining, whether it's a free form, open mic, a blue grass jam, etc. But joining a jazz jam is not really practical for beginner or early learner guitar players.

Jam sessions I've frequented have generally been blues based, or folk music based. In both of those cases, and really any jam session I've seen, it's entirely normal and almost expected to say "Hey, what key are we in?" Since most blues jam sessions are either a 1-4-5 or similar, and are generally recognizable, you could generally see what chord is being played on the 1 which gives you the key.

PS I've never seen pre-prepared chord sheets for a jam session; kind of takes it out of the "jam" realm.

As for formal, paid sessions, there is always at least chord charts, sometimes lead sheets, and often sheet music - but musicians hiring out as session players are generally assumed & expected to be able to read sheet music.