do you have to credit quiz questions that you found at another website and added to fan pop.

you dont have to credit the quiz questions..
if you want to you could put a link to the original in a comment.or credit the maker in the trivia section.

i personally think its lame to copy and paste quizzes. in my opinion you should at least take the time to phrase the question in your own words, add a fitting image etc
im sure some of the quizzes i have asked have been asked on other sites- not because i copied them there but because asking e.g. aboot the name of a pet is sort of an obvious question.

i have found quizzes on here where people copy and pasted the question (including the typos :S)- in my opinion its more fun to answer questions where the quiz maker thinks of funny ways to phrase the question, or thinks of great options (like one of my faves from sualey asking if josh radnor is allergic to the little piping that you get on the edge of birthday cakes.) and "personalizes" the quiz that way.
copying and pasting seems medalwhorish (yeah! thats a word) but hey thats just my opinion.

You don't have to credit a quiz question that you found elsewhere however if it is a difficult one or a conpkiacted one or a clever one, you could always just say "Thanks to....blahblah for the question" in the description =)