Where at Trapper Creek is a great place to view the mountain? I don't recall a specific great place for a "lookout" view of the Mountain. Yes, Trapper Creek is about mile 115. I stayed in Trapper Creek once and also drive by there a lot to/from Denali. At least in Talkeetna you have that nice overlook coming into town.
While not a formal lookout, one spot to catch a (weather permitting) view is where the Parks Highway crosses Trapper Creek itself. That's right around milepost 115 and just before the pizza pub run by the entertaining German woman. And if the weather seems cooperative, a drive out the Petersville Road from Trapper Creek can provide lots and lots of photo ops.