The console is your friend. What I would do is type dataLayer
into the console after dataLayer.push, then click on the last object in the array and you'll see your values.
For instance, I put the dataLayer.push on an onclick event and ran dataLayer and was able to see this come through. Granted they are static values, but you get the idea.
UPDATE:
Google Tag Manager has updated their debugger, allowing you to see both Names
or Values
being passed into GTM.