The Witcher 2: Assassins of Kings 
Edit
While Nekker claws are mainly used in alchemy, they can be used as one of the components needed to craft the Armor of Ys and Blasphemer's armor.
The Witcher 3: Wild Hunt Edit
Nekker claw is an alchemy ingredient but is not needed to craft anything. It can be dismantled into a monster claw.
