Jewel of Kajaro

The Jewel of Kajaro is a neck item for mages which gives a bonus to stamina, intellect, spirit, and overall magical power. The jewel is part of the armor set called the Illusionist's Attire.

Source
The jewel is a reward for the quest given by one of the trolls on Yojamba Isle in Stranglethorn Vale.

Note that this quest is the end of a quest chain that starts off with Pebble of Kajaro which yields an uncommon version of this amulet (to be obtained at friendly reputation with the Zandalar Tribe). With each new reputation level gained (honored, revered and exalted) this item can be upgraded for free at Yojamba Isle (transforming the uncommon amulet into a rare one for honored and revered and into the epic Jewel of Kajaro at exalted).