Talk to the Sith Soldier guarding the Sith Academy on Korriban to learn that Yuthra Ban is at the bar and is accepting students for the academy, At this point there are two ways of trying to enter the base. The first is trying to persuade Yun to allow you in. However, this requires a high persuasion skill. The second is a lot quicker and once done, persuading Yun to allow you inside the academy should be easy. Instead of entering the bar to talk to Yun, go back to your ship, An intermission sequence and dialogue showing some Sith graduates trying to start a fight with you will start. No matter what happens, you will have to fight them. Defeta them and look at their remains. One of them will have a Sith Academy Medallion. Pick it up and talk to Yun.