How do I know what version of Skype for Windows Phone I'm using?
The latest version of Skype for Windows Phone 8 depends on which version of the Windows Phone operating system you are using (Windows Phone 8 or Windows Phone 8.1).
If you're using Skype for Windows Phone 8, the latest version will be 2.22.x (the "x" representing further development, like tweaks and bug fixes). Skype for Windows Phone 8.1 will continue to develop new features and functionality, and the version number on the app will be different (you can check the features and the latest versions of the apps released here).
However, if you're using Windows Phone 8.1, your Skype will have extra features, like the ability to use Cortana with Skype and the Video Upgrade (preview).
To find out what version of Windows Phone you're using:
On your Windows Phone, tap the settings tile.
Under software, you will see either Windows Phone 8.0 or Windows Phone 8.1.