Pandaren hunters automatically know how to tame Cloud Serpents. Hunters of other races must learn the skill 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.
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.
*Level scaling: In Shadowlands most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.