Ulfang has asked you to collect the Eyes of the Eagle. Return to him in disguise in the Rivenwood after you have done so.
If you somehow lose the Worg Disguise, return to Sage Mistwalker for a replacement.
Garwal hides himself behind an unnatural magic. None can see him unless he wants you to. There may be one chance we can take, though.
My enemy, the great eagle, Talonshrike, is said to have eyes that can see anything. If you were to take her eyes, then you would surely be able to see Garwal.
Talonshrike keeps her nest at the base of a waterfall just to the southwest of the vrykul place called Skorn. If you touch the eggs in her nest, she will come down from the sky to kill you.
Get her eyes.