Please follow the steps below to find the version number of ZenUI in your phone:
1. Go to "Settings" > "Apps" and press the settings icon on the upper right corner of the screen.
2. Select "Show System" to show all the installed Apps and the system files on the list.
3. Find "ZenUI Launcher" on the list and press the icon to see the App info.
4. You will see the version number of ZenUI under the name of ZenUI Launcher. ex. in the picture below, the ZenUI version in this phone is 4.0.0.