There currently is one option to travel by night train from Padborg (Denmark) to Prague (Czech Republic), taking approximately 9 hours: Namely the RJ 387. These lines are operated by Deutsche Bahn and České dráhy.
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.
České dráhy (ČD) is the Czech national railway operator, running domestic and international passenger trains connecting the Czech Republic with neighboring countries.