Stalker's Bone is an item found within Darksiders II.
Stalker's Bone is the first item collected in the Shaman's Craft Side-Quest. After speaking with Muria in Tri-Stone, track down Karn, located at the end of The Charred Pass, just outside of The Cauldron. Speak to him and he tasks you with collecting Stalker's Bone.
Death does not need to begin the Shaman's Craft quest at the start of the game. Anytime throughout his journey, Death can speak with Muria and then Karn to trigger the start of the quest. Stalker's Bone can easily be acquired by defeating any Stalker in the overworld, in which a few can be found within The Fjord of the Forge Lands.
After collecting Stalker's Bone, speak with Karn once again and you'll then need to find the second item in Shaman's Craft, Mordant Dew.