There currently is one option to travel by night train from Kolding (Denmark) to Prague (Czech Republic), taking approximately 10 hours: Namely the RJ 387. These lines are operated by DSB, Deutsche Bahn and České dráhy.
DSB (Danske Statsbaner) is Denmark's national railway company, operating passenger trains across Denmark as well as connections to neighboring countries.
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.
These trains only have first and second class seats. The cars remain lit throughout the night and the seats cannot be reclined.
ČD, the Czech national railway, operates domestic and cross-border passenger trains linking the Czech Republic with its neighbors.