Well there isn't something EXACTLY like yahoo answers, but there are similar systems. Such as these:
https://vborg.vbsupport.ru/showthrea...hreadid=165673
https://vborg.vbsupport.ru/showthread.php?t=170419
These would be in addition to what is already available in Vbulletin, which is the ability to create a forum, post threads (or questions) and then get people to reply.