Parentheses work much the same way as quotation marks. If the question is being asked within the parentheses but not the whole sentence, then the question mark would appear within the parentheses to highlight this. If, however, the question was being asked as a whole and parentheses were being used to simply add more information, then the question mark would appear outside the parentheses. It would look like this:

Chad was looking at me (or was he?). – here the question is only being asked within the parentheses so it is inside the parentheses that the question mark must appear.

Was Chad looking at me (he might have just been avoiding looking at the sun)? – the question is asked as a whole so the question mark appears outside of the parentheses because the information provided within the parentheses isn’t a question, it’s just additional information.