VWP use has some conditions associated with it, and some of the conditions associated with VWP use are why CBP may ask to see the itinerary. While it shouldn't hurt to ask to speak to the supervisor -- it may -- and it's likely that the passenger would end up speaking to a supervisor of some sort if the initial encounter with the CBP employee asking for the itinerary doesn't meet the satisfaction of the initial CBP employee and/or whoever is doing the secondary.

Sometimes coming across as playing along works better than trying to use a hammer to hit back.

Showing emails or PDF files from a laptop or phone are certainly allowed in the CBP clearance facility if the CBP wants to see them and demands them.