There currently is one option to travel by night train from Kufstein (Austria) to Wittenberge (Germany), taking approximately 10 hours: Namely the UEX 1304 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.
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.