I'm doing yahoo PPC but sorry didn't catch your question.

You mean not to show up on Bing but just Yahoo?

For eg. I see one question/answer that ranks in Google. Can I set it up in Yahoo ppc to advertise ONLY on that page only?

you can do that on bing ads. on excluding bing.com on your settings

Guys the OP is not asking whether it is possible to be shown only in Yahoo search results. The question is whether it is possible to have your ad shown on only one of Yahoo's properties, in this instance even under a specific question on Yahoo Answers.

I'm pretty sure Yahoo Answers uses the BingAds display network so that is where you want to look. You might be able to specify that you only want your ad displayed on the subdomain answers.yahoo.com, but I imagine that is as specific as you can get.

If you target things in the right way you should be able to be shown on the specific page you are interested in, but you will also be shown on other answer pages. I've never done any display advertising so this is as much help as I can provide.

Any experienced Yahoo ppc user?

The question is to know if advertising ONLY on SPECIFIC Yahoo question/answer page is possible?