Welcome to the Wefugees Community and thank you for your question.
I made some research and found this website on marrying in Denmark. Here it is written "Passport or ID-Card". They don't specify if a travel document for people with subsidiary protection will also be accepted. I would recommend you to contact the publisher of that website directly, as they seem to be experts. You will find their contact details and a list of the other required documents following the link.
All the best,