You must learn a special skill to tame Cloud Serpents, which is different to the skill required to tame other Lesser Dragonkin. Pandaren hunters gain the skill automatically, but hunters of other races must learn it from the tome How to School Your Serpent, which may purchased from San Redscale at The Arboretum in The Jade Forest. You require Exalted standing with The Order of the Cloud Serpent to read this tome, but the learned skill is account-wide. You can even purchase and read this tome on a non-hunter character.
Location & Notes:
Located in Vale of Eternal Blossoms. Normally friendly, but can be tamed if you use the toy "N'lyeth, Sliver of N'Zoth" while in War Mode. The Ivory Cloud Serpent appears only during Mogu Assaults. The Ivory Cloud Serpent spawns every ~1.5 - 3 hours at coordinates ~ 27,55, at roughly 2-3 times the height of the trees, and flies rapidly in clockwise circuits around the zone. The best place to tame it is at the southern end of the roof of the Gate of the Setting Sun.