Embersilk was introduced from the Cataclysm expansion, so only humanoids between levels 81 to 87 will drop Embersilks. Some of the best places to find Embersilk in WoW include:
A good place to find embersilk in world of warcraft is Mount Hyjal, where you will find Flamewakers near the daily quest Molten Front. Each kill will drop between 1 to 3 embersilk and spawns relatively quick. Check out the map to see the exact location.
Twilight Highlands is also a good place to find Embersilk in WoW. The Glopgut Ogres at Glopgut’s Hollow will drop between 2-6 embersilks after each kill. The ogres might be slightly harder to kill but they do reward accordingly. See below for the exact position.
Another best place to find Embersilk would have to be Uldum. The location is northwest of the map Uldum, Obelisk of the Moon, there is a place called Chamber of The Moon. If you have done the quest here the humans will not spawn any more. But if you haven’t done the quest, this place is a gold mine for embersilk. For the exact location of the chamber see the map below.