There currently is one option to travel by night train from Bischofshofen (Austria) to Bonn (Germany), taking approximately 12 hours: Namely the UEX 1310 operated by UEX.
UEX (Urlaubs-Express) runs seasonal night trains and car-carrying trains between Germany and Austria.
Options range from seats and shared couchettes to private couchette compartments, sleeper compartments and connected sleeper cabins.
Cars can be taken on the train at the car terminals only, and the vehicle is booked together with the ticket.
There is a free ski compartment. Drinks and snacks are available in the bistro on board.
Children with their own seat or bed pay a reduced fare.