It depends. If you have a view of MK, then you definitely can see the fireworks. But, if you are down on the other end (Big Pine Key) it would be harder to see them.
You can always walk over to Gasparilla Grill and watch them! It's a perfect view from there.
Tell the reservations folks at the GF that you'd prefer a MK view. It may not help, but it can't hurt. It's worked for us in the past, anyway.
And I concur: the area just outside the Gasparilla Grill, by the marina, is a SUPERB spot for fireworks viewing. So is the area by the boat dock, by Narcoosee's.
It depends on what building you're in, and if you have a MK view room. I think Boca Chica's MK view rooms have great views (as do the Main Bldg)! Otherwise, just walk over to either Gasparilla or Narcoossee's deck, as the others have said!