With the car:
Autobahn A 8, exit Piding or A 10, exit Grödig. Follwo the signposts to Berchtesgaden. At the bus termainal in Berchtesgaden follow the signpost to Königssee.
Straight ahead untill you see on the left side the signpost Dorf Königssee. Turn left, after 200 m right and the next road left.
Via Freilassing to Berchtesgaden station and from there either by Taxi or by bus (10 Minutes).
This link leads you direct to the website of the German Railway Agency.