9,93 GB of 5 GB iCloud storage taken up by Docs - how to find an delete them? How is that possible?
How can I locate these files and remove them?

I cannot locate them neither through the iOS Settings nor at https://www.icloud.com/.

All I am using iCloud for is creating a backup with only a small number of applications included and it is usually smaller than 2 GB.
I was unable to solve the problem myself, so I contacted Apple Support. During a phone call, I was explained that the space was taken by temporary, hidden files like incomplete backups. 

I couldn't delete these myself and the technician did that for me.