I installed an app and I would like to know what is it version. In the app menu no command is available to see the version.
If you go to the Store, select downloads from the menu, and go to History, it will show you the latest version of an app you have installed. I know this works in 8.1.1 DP, but I haven't checked it in 8.0.
The closest you can get is post a comment in the Store, wait it appear anew check the version it says you are using.
As you can see I posted a comment using the version 126.96.36.199 while the current version is 2014.822.316.3341.
Those versions are not extracted from the same place (I think). But this particular developer use the build number as reference. In this case 236 in my comment and 316 in the app details page.
You can only ever have one version of an app deployed at once and you can find the currently released version number by going to the store, browsing to the app in question, swipe across to the details tab, and you will see the date of last update, and the current version number