This quest is not available in game.
Use the Shimmering Vessel on the Blood Elf Magisters to fill it and return to Knight-Lord Bloodvalor in Silvermoon City.
Take this vessel, <name>. The enchantment it bears will allow you to draw the last vestiges of the Light surrounding these magisters. They once tended the captive naaru and some of its energy yet remains within them.
It will be just enough to restore your comrade to life.
Do not worry about the magisters, <name>. I have seen to their care, and Lord Solanar assures me that Lady Liadrin seeks a new source of power even now.