So I'm in Folgunthar. I clear it out. Kill the last guy and he has the arrow marker on him. Yet I can't loot him. Which makes it so I can't get the next step in the line to know where the other person is buried. Anybody else have this issue on this quest line?

Try re-doing the fight?

Sometimes the dead enemies sink into the environment and you can't interact with them.

Reload, (your going to have to redo the entire dungeon)

Leave the area, and wait for at least a day then go and retry