Looking on the internet deeply has found these results:

Cheat in exam is the most popular phrase on the web.

Cheat on exam 121,200 results on the web	Cheat in exam 131,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	I think the captain cheats on his eye exam. My mom wouldn't cheat in my dreams. Once you cheat in a marriage, there's no going back. I believe Knight Valiant is using a magic shield to cheat in the tournament. "It would be inappropriate to cheat on an exam, even if it meant I would get a better grade." Agree. Three men called me a cheat in a Kansas City card game. You can't cheat in sports and get away with it. Did you cheat on your exam?

Cheat on exam

121,200 results on the web

Cheat in exam

131,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

I think the captain cheats on his eye exam.
My mom wouldn't cheat in my dreams.
Once you cheat in a marriage, there's no going back.
I believe Knight Valiant is using a magic shield to cheat in the tournament.
"It would be inappropriate to cheat on an exam, even if it meant I would get a better grade." Agree.
Three men called me a cheat in a Kansas City card game.
You can't cheat in sports and get away with it.
Did you cheat on your exam?