I had to do the same here and the above works except I had to provide login details as it was a local docker repository.
It is as per the above but with supplying the username/password in the URL.
curl -k -X GET https://yourusername:yourpassword@theregistryURL/v2/_catalog
It comes back as unformatted JSON.
I piped it through the python formatter for ease of human reading, in case you would like to have it in this format.
curl -k -X GET https://yourusername:yourpassword@theregistryURL/v2/_catalog | python -m json.tool