When you are talking about specific items, then you would use "in". "There are several difficult questions in the exam." But when you are generally dealing with things as a topic of discussion, then you would use "on". "While we are [on] the subject, what did you think of the movie." "He made a good point [on] the question of economics." "He has several opinions [on] the issue." "He did poorly [on] the exam." "We've made several advancements [on] equal rights for everyone."

Both would work... If you're on site where English is the focus, everyone is going to be concerned about right or wrong... If you're telling your friends about the results, nobody will care and either would pass unnoticed... Both are fine. Your choice of preposition (in or on) might indicate a slight difference in how you (the speaker) perceive the experience of the exam but that's PERSONAL MEANING, and there is no right or wrong (in this case) Sometimes in / on have different meanings -- not in this case. If the exam was an accreditation exam where, for example, you are a pharmacist and you're doing role plays with patients and being graded on your English (this is how it's done in Canada)... where you're actually in a room, with people, doing stuff, being graded...then you might use "in the exam" because you were "in" an exam SITUATION. If it's just a paper test, you might say "on the exam" There is just a slight difference in nuance and tone, and it's personal. Everyone would interpret it differently and none would be wrong. Hope that helps.

"on"

I got a good score on the exam.

It's "in the exam", not "on the exam", and please allow me to add that in English I guess you should say "I got a good mark in the exam". Hope that was helpful!:)