1. Add the admob plugin to your cocoon project.
<cocoon:plugin name="cocoon-plugin-ads-ios-admob"/>
<cocoon:plugin name="cocoon-plugin-ads-android-admob"/>

2. Add cordova.js to your index.html above your other scripts.
<script type="text/javascript" src="cordova.js"></script>

<script type="text/javascript" src="game.min.js"></script>

3. Title Screen for example.
TitleScreen = ig.Game.extend({
	
    // ...

    rdy: false,
	
	init: function() {

		// ...

		if (ig.interstitial) {
			ig.interstitial.load();
		}
		else {
		    ig.interstitial = Cocoon.Ad.AdMob.createInterstitial("ca-app-pub-XXXXXXXXXXXXXXXX/NNNNNNNNNN");
		    ig.interstitial.on("load", function(){
		        ig.interstitial.show();
		    });
		    ig.interstitial.on("fail", function(){
		        ig.game.interstitialCall();
		    });
		    ig.interstitial.on("show", function(){
		        //
		    });
		    ig.interstitial.on("dismiss", function(){
		        ig.game.interstitialCall();
		    });
		    ig.interstitial.on("click", function(){
		        ig.game.interstitialCall();
		    });
		    ig.interstitial.load();
		}
    },

	update: function() {
	    // ...

	    if (!this.rdy) { return; }

	    // ...
	},

    interstitialCall: function() {
        this.rdy = true;
    },
	
	// ...

});

Now, each time on the titlescreen the ad will called.