It looks like the certificate being used by the Docker registry is not valid (according to your Docker client). You have a couple of ways to fix this:
- Add a self-signed certificate to the Docker client
- Add the registry as an "insecure registry" to ignore the certificate issue
- Use a valid, recognized certificate
The third is the ideal method since #1 and #2 would need to be done for any client you use with that registry. If you have control to do #3, I would recommend getting a valid cert (LetEncrypt lets you generate one for free) and using it.
It is also possible, though less likely, that you are using a proxy or VPN that is between you and the registry and that has a certificate the client has a problem with. If that is the case, you can verify by trying to access it without the VPN/PROXY.