However, duties of a PhD student vary a lot. I am not sure about Denmark but in Germany, CS PhD students usually work as full-time employees at the university.

However, duties of a PhD student vary a lot. I am not sure about Denmark but in Germany, CS PhD students usually work as full-time employees at the university.There is no grad school¹. You are expected to balance your PhD research (realistically, 25 % of your time), teaching (50%), and misc. obligations (20%). ¹ There are a few dedicated grad schools at some institutions. However, these are the exception, not the norm.