I've found a solution....
For those interested in rewarded videos or just using the original "cordova-admob-pro" you can add it using Intel XDK and In your Construct 2 add the Browser object then add an action: Browser -> Execute Javascript: "AdMob.prepareInterstitial( {adId: 'ca-app-YOUR-ID', autoShow: false, overlap: true})"
and then later: "window.AdMob.showInterstitial();"
In other words: you don't need this plugin... You can use the "original cordova functions".
(this might sound normal to you but I'm new to construct and just found out about this...)
You can see the entire documentation here: https://github.com/floatinghotpot/cordova-admob-pro
Thats why the plugin was made, to save you the work to write all the javascript functions. Obviously this is only a wrapper, and without the Cordova plugin admobpro you do nothing. The function showInterstitial is not for rewarded videos... The C2 plugin and the Cordova plugin have a function to do it.