Zandalari hunters automatically know how to tame Direhorns. Hunters of other races must learn the skill from an Ancient Tome of Dinomancy which is a rare drop from Zandalari Dinomancers on the Isle of Giants in Pandaria. This skill is NOT account-wide.
Located in Savagelands, Zuldazar. Only present when the Kua'fon daily quest A Nose for Ptrouble is active. There is a 1-in-4 chance of this. If Kil'Tawan is still not present, try killing Thunderfoot or Azuresail, and she may spawn.