The version shows up in the console shortly after you load the plugin with the “require” line.
The version listed by grcool are correct. I asked Appodeal for a list of my apps and what version they were using and they provided a list in a few hours. They should be able to do the same with your apps.
07-20 21:42:40.483: V/Corona(18606): > Class.forName: plugin.appodeal.LuaLoader
07-20 21:42:40.484: V/Corona(18606): < Class.forName: plugin.appodeal.LuaLoader
07-20 21:42:40.484: V/Corona(18606): Loading via reflection: plugin.appodeal.LuaLoader
07-20 21:42:40.485: I/Corona(18606): plugin.appodeal: 1.6.5b (SDK: 2.5.3)