On Vox, also two Santug sitting in PoK. Tried checking the Rathe Mountains to see if it was perhaps fixed for home cities but there are also two of him there. He won't give out the quest where he check's his list and rewards with a present.
Just wanted to add/confirm that myself and a guild mate are also unable to complete "Frostfell - Santug's Gift" and that there are double Santug NPC's in PoK and Crescent Reach that i've noticed in passing.
I was able to say "Check your list" and get the gift. If you hail him you get a response telling you to talk to the others about doing tasks.