Badge of Vows 20 is a quest item from the From A Different Sky - Part 2 DLC. Merely picking it up satisfies the goal needed to complete the quest.
Gran Soren in The Everfall during pre-game or NG+. It's on the fifth level's underground pillar. Position yourself at the stairs going down from the fourth Level to the fifth, jump on the edge and over to the rocks on your left, then Double Vault or Levitate to reach the Pillar.
Note: When you are on those rocks, there are coins and chest in the area behind the rocks.