in the top right hand corner on the question, there is a word in blue letters that says "next" with a little arrow. if you run your mouse directly under that area, a red flag will pop up. click on that and the report page with pop up. read it carefully to be sure you are reporting correctly because it is illegal just to report things you disagree with or that you are personally offended with. you have to be sure the person you are reporting has actually broken the rules of yahoo's community guidelines. if you have not read them, do so before you report someone. you can put comments in the comment section and then click on report or send at the bottom
once you have reported them, yahoo will send them a notice that their question has been reported and they will have the opportunity to refute the report. if yahoo managers find you reported them in error, they will take some of your points and/or delete your account.
if they are found to have posted an errant question, their points will have 10 pts removed and they will loose some standing in the community. eventually their account could be deleted if they are reported too often.