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 Mistfall Village, 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. Appears in the Assaults phase of the zone, during all Assaults. Hovers near the entrance to the Silent Sanctuary.