Where can tauren learn two handed swords in wow?

The use of 2-handed sWords is part of your Class. Warriors, Death Knights and Paladins can use 2-handed sWords and thus to use those your Troll will have to be one of these classes.

Hunters can use 2-handed sWords as well, but they will lose this ability in Mists of Pandaria, when Hunters become a ranged-only class.