I saw someone ask this before, but I don’t remember the answer, and search didn’t help.
Is there a way to search by link?
For example - There are multiple John Smith’s on Discogs. And multiple John Smith’s on MB. Can I search MB to see if John Smith (69) is connected to a MB artist?
URL search is not supported by MusicBrainz for now. There is a request for this feature you can vote.
However, third-party murdos’ Discogs import userscript does exactly what you are looking for: search for an MB artist with an URL to the current Discogs artist.