Where can I see on which domains my license is being used?

Open your Greyd.Suite dashboard (on a site level, not in the network administration) and go to the tab "license" to see all details with regards to your Greyd.Suite license.

You will first be asked to enter your license key again for security reasons.

Then you will get an overview of all domains your license is currently used for as well as additional information such as the license plan, number of domains activated, etc.