Sharpbeak was not with the Witherbark trolls. Perhaps the Vilebranch trolls took him. Go to the Altar of Zul on the western edge of Vilebranch territory and search for the gryphon child.

Check the top of the Altar of Zul, then return to Gryphon Master Talonaxe.

Return to Gryphon Master Talonaxe at Aerie Peak in The Hinterlands.