He wanders around the planning room, which contains a map of Skyrim and a small library of books. He can sometimes be found sitting on one of the benches to the immediate left or right of the room, making it difficult to sneak up on him.
During the quest, Lieutenant Salvarus is aboard The Katariah and is one of the Emperor's guards along with Captain Avidius. They are at different quarters of the ship. Both of them can be killed and looted, providing the Katariah Master Key which unlocks the Emperor's Quarters.