Customers using an on premise instance have no way to know what's their registration status besides using the admin center in JSF UI
Launch nuxeoctl register --status
A message is returned:
Your Nuxeo Online Services registration is valid until [date].
You don't have a valid Nuxeo Online Services registration. Launch the nuxeoctl register command to register this instance.
Command can be ran while server is started (just like the register --renew command)