There are a few ways to find out the Unified Service Desk version that is installed.
For the Client, in Windows under Programs and Features, you will see Unified Service Desk. To the right, you will see the version number:
Also, logging into USD will display the USD splash screen with the version number:
After logging in, you may have the option to open the About window. To do this, go to the Settings->About menu, and the following screen will open, with the the version information:
For the server, go to Settings->Solutions:
Find DynamicsUnifiedServiceDesk. You will see the version, in this case, 18.104.22.1689:
And the UII version: