Someone put tile on top of a granite floor? They probably sanded it first with an abrasive so that the thinset would adhere. At least, that would have been the correct way to do it. There may be millions of tiny little scratches in the granite holding on to the thinset residue. Depending on the thickness, it may or may not be able to be ground down to a nicely polished surface free of residue and scratches. Finding a restoration contractor with the equipment to do that may not be easy. It certainly won't be inexpensive. If this is a budget effort, the best approach may be to remove the granite tile layer as well.

Of course, if they did it incorrectly, then that might just be thinset residue without the bottom layer being being abraded. In that case, you have nothing to lose to try some grout haze remover and substantial elbow grease on a spot. If it works, you'll at least see the amount of effort ahead of you, and decide if demo or cleaning is gonna be your choice.