There currently is one option to travel by night train from Schwarzach im Pongau (Austria) to Cologne (Germany), taking approximately 12 hours: Namely the UEX 1310 operated by UEX.
UEX (Urlaubs-Express) operates seasonal night trains, including car-carrying trains (Autoreisezüge), from Germany to Austria and back.
You can choose a seat, a couchette berth, a whole couchette compartment, a private sleeper compartment or connected sleeper cabins.
You can bring your car, but only between the car terminals, and you book the vehicle along with your ticket.
There is a free ski compartment. Drinks and snacks are available in the bistro on board.
There is a reduced fare for children who have their own seat or bed.