how do you find the key to the generator in the hotel?
there isn't a singular key for "the" generator, there's three keys in total on level 3.
First one is found by going in the vents to the right after entering the level
Second one is in the room(s) on the bottom side of that T shaped room with the trapdoors
Third one is in the big trapdoor room unlocked by the steam pipe room that's on the far side of the long hallway with electrical wires