Do you mean brackets [ ] or do you mean parentheses ()?
If parentheses, then you use end punctuation (a period or a question mark) within the parentheses only the whole sentence is enclosed. Otherwise, not.
For brackets, normally, you use punctuation as if the brackets weren't there. If you are talking about end punctuation, like a period or a question mark, then that depends upon what is inside the brackets. If it is a question [what kind of question?], you can put it inside the brackets as well as putting sentence punctuation outside.