How can I see which tenant(s) my user belongs to?

If your user belongs to more than one tenant, then you will have an option called “Tenants” when clicking on your login name in upper right corner of the Portal. Clicking on this option will show a list of all tenants your user have access to:

You can switch between the different tenants by clicking the tenant you want to work in.

If your user has access to one tenant only, then you will see the name of this tenant instead of “Tenants”