I get confused about the usage of do well in/at/on something

Is it true that we use

Do well on something for exams
Do well in something for courses
Do well at a place or event

I need a complete explanation pls

Rose. I'm afraid that if you expect a "complete explanation" of something as idiosyncratic as use of prepositions, you are going to be disappointed.

It may vary between regions, between individuals, in idioms.

I would say

• "do well at ..." a general activity (French, football, painting, science, carpentry),
• "do well in ..." a specific activity (exam, competition, interview)

I think the only time I would say "do well on ... " would be an area of knowledge, where it would mean much the same as "do well at knowing about ... ".

But I think if you ask other English speakers, you may get a different answer.