Destroy the source by clicking on the pole at ( -1128, -523, -1656 ) /waypoint -1128, -523, -1656. The pole is hard to see. If you have wings or a glider mount, fly to the ledge behind the pole (the highest ledge), then drop down to the ledge just above the pole carefully. It is possible to destroy the pole without drawing aggro from the guardians.
Return to Jel'ziz Amun at ( -1385, -533, -2275 ) /waypoint -1385, -533, -2275
The location of this update was changed after the 3/8/2011 hotfix. From the patch notes: "The magical focus for the quest "Power From the Tower" has been moved outside. This is to make the quest more easily soloable, and bring this quest in line with the other Deepwater Circle quests."
The reward "Deepwater Circle Highboots" is an appearance only item.