This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Using the Glyphs of Summoning, summon and subdue a voidwalker, then return the Glyphs of Summoning to Gan'rul Bloodeye in Orgrimmar.
Now, observe the Tablet of Verga, for it contains the glyphs you will need for the summoning. Take them to the circle in Neeru Fireblade's tent on the other side of the cavern. There you will be able to call for the voidwalker.
You must defeat it using whatever physical and magical means you have at your disposal. When this is completed, return to me with the glyphs of summoning and I will demonstrate how you may bind the creature to your will.