Darth Vader only lit his lightsaber once during the construction of the Death Star when he was in the context of enforcing the Emperor's will and commanding the work on the station. However, if you're referring to lightsaber duels or battles involving Vader on the Death Star, he faced multiple opponents across different stages of the film series, particularly in "Star Wars: Episode IV - A New Hope."
If you meant to ask whether he only confronted a single foe in a lightsaber battle on the Death Star itself, that would pertain specifically to his duel with Obi-Wan Kenobi in "A New Hope." If you have a different context or scenario in mind, please clarify!