Night train from Copenhagen to Hamburg
There currently is one option to travel by night train from Copenhagen (Denmark) to Hamburg (Germany), taking between approximately 6 and 7 hours: Namely the EC 1195 operated by DB.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night. In these night trains, there are only first and second class seats. The lights stay on all the time and there is no way to recline the seats.