I don't remember who it is, but all you need to do to know where to go for the next rank is to talk to the previous trainer, they'll tell you where to go for more training. Also, can't tell you who to go to as you didn't say if you were horde or alliance, so just check out this list: http://wow.allakhazam.com/db/guides.html?guide=361
You can find it yourself on the bar to the left, down near the bottom.