There are multiple ways to find the version of your QuickBooks Point of Sale Desktop.
First, the version can simply be found on the very top of the application...
Also, if you are looking for the version and update release, you will need to follow these simple instructions:
Click "About QuickBooks Desktop Point of Sale"
In the image above you see the bold line noting "QuickBooks Desktop Point of Sale 18.0". However, if you go down 5 lines you see the line noting "Release 18.0 r5".