I just figured out, how you are able to retrieve the Musicbrainz Id (MBID) from a specific Discogs Release. The following link can be used:
Obviously for the XXXX you need to put the release-Id of the release in discogs.
The Discogstagger2 contains a small script (scripts/find_mb_ids.py) which calls the above mentioned url and puts the determined mb-id and the given discogs-id in a file. This script is based on an existing id.txt, which I do use to determine the discogs id for each releaase i own.