Kill all three of the Sha'ir to breach the destructible wall at ( 83, -9, -96 ) /waypoint 83, -9, -96. Upon the death of the third one, a red-text emote will display on your screen confirming that the wall has been destroyed.
Once upon a time, the three Sha'ir in the zone had to die within about 10 sec of each other, or else they would respawn and the wall blocking off Lockjaw wouldn't break. This is no longer the case as of 2009 (confirmed to still be true as of 9/4/2010), though the Sha'ir will still respawn and red text will still pop up informing you of their reappearance. Just ignore the text and kill them at your own pace. Once all three have died once, the wall blocking the northernmost hallway will break and you can move on to Lockjaw himself.