What exactly do you want/need to handle there?
Does it really matter who asked a question, as long as the question is a good fit on the site and it is clear, you can upvote it, else don't or consider downvoting it (but I do always suggest you leave a comment on why you think it deserved a downvote). I don't think you should even consider looking as who really asked it, that is rather irrelevant I would say.
With regards to duplicate questions, if you feel a question is a duplicate of another (again, irrelevant if they were posted by the same or a different user), just flag it as a duplicate. If others agree, it will be closed as a duplicate (requires 5 user votes or a single moderator vote).