From wow.incgamers.com

The Violet Eye faction was introduced with Karazhan - you start as Neutral and get first reputation increases by doing quests leading to getting a key to Karazhan. Those quests start at Karazhan (2 of them), after completing it continues to Dalaran where Archmage Cedric is now located. And finally to Shattrath City to see Khadgar.

Getting key for Karazhan involves Shadow Labyrinth in Auchindoun as next step.

It is possible to purchase a Karazhan key from beta temporary vendor - when it's up (disappears when server restarts) you can find him in Shattrath just next to Khadgar.

History of the Faction

The Violet Eye is a secret sect founded by the Kirin Tor of Dalaran to spy on the Guardian of Tirisfal, Medivh, in his tower of Karazhan. Though Medivh is dead, the Violet Eye remains in Karazhan, defending against the evil that appears to have taken hold in the absence of its master.

It is unknown whether Khadgar, Medivh's apprentice, was a member of the Violet Eye or had any knowledge of its activity.