It will show on a patrol beacon across from the Forge cliff with a small ghost symbol over it when you take your ghost out. The actual mission requires going down into the sub structure under the Forge and defeating a spider tank. The scan is the area where the tank is sitting. If nothing shows in the whole area when you take your ghost out it's either because you have done all the patrols in that area for this round or you have an active patrol that you are still working on. If you don't have an active patrol go to orbit and come back.

You in the right place? Drop down in to archons forge and head down the passage that's behind the boss spawn area. Keep going until you are blocked by lasers. Use a splicer key at the terminal on the left to go through. You'll come to a room with an axe. Grab it and head down stairs to the Walker. Charge the axe at the fire so you can RT the walker to bits. Kill the adds and scan the wolf head on the ground where the walker despawned.