Is it rude to make 问题 about users?

Its REALLY rude,

But without them knowing 或者 finding out

If they know about it beforehand and they say it's okay,and as long as the 问题 are not too personal it should be fine.If they don't know about the questions,then yes,it is kind of rude.

Not really, I tell 你 its perfectly fine! Except to just go to the right place to do it! c:

It depends. Though, it's better to just not make 问题 about other users.

Well I guess it just all depends

Depends on the question.

if it isn't insulting, inappropriate, 或者 done with the wrong intentions/outcomes then i believe it is fine

I would say it is.

If 你 have a 问题 about a specific user, just ask them privately rather than putting them on blast.