Main Version
The version of Paratext is shown in the upper-left corner of the Paratext window:
Paratext 9 (and higher)
Paratext 8
Minor Version
You can also find the specific/minor version of Paratext that you have installed:
Paratext 9
- Go to the Paratext menu > About Paratext:
Paratext 8
- Go to the Help menu > About Paratext: