There currently is one option to travel by night train from Ringsted (Denmark) to Prague (Czech Republic), taking between approximately 11 and 12 hours: Namely the RJ 387. These lines are operated by DSB, Deutsche Bahn and České dráhy.
DSB, Denmark's national railway, runs passenger trains throughout the country and connecting services abroad.
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.