The Non-Canon Expert explains why Darth Vader, one of the most powerful Sith Lords in the history of the Order, was reliant on an Imperial Interrogation Droid to torture Leia for the location of the stolen Death Star plans and Rebel base, rather than just simply use the Force and the dark side abilities of Drain Knowledge.
This is a Legends story for Darth Vader and Leia with information found primarily in the novel «Death Star» by Michael Reaves and Steve Perry. I hope that you enjoy it!