Vertok Axebreaker in Thrallmar wants you to bring Bonechewer Blood Samples to Apothecary Zelana at Reaver's Fall.
Apethecary Zelana has been studying the beasts of Hellfire Peninsula in the field. She wants a sample of the blood you gathered for; with luck, she might discover what turned those bonechewer bastards' skins red!
Zelana is at Reaver's Fall, southeast of Thrallmar. Follow the road east and when you see a destroyed, green-glowing hunk of metal, you're there. She has a camp set up behind the wyverns.