Using electronic drums with headphones is about as quiet as drum practicing can be. That doesn't mean it's always quiet enough for every environment, it just means it can't be much quieter.
One of the biggest problems that still remains with an electronic drum kit is that the action of the kick pedal on the floor can make a surprising amount of noise in the space below the floor. This means that getting a basement apartment in a building is very helpful in avoiding disturbing your neighbors.
The second biggest problem of electronic drums is the sticks on the pads still make some noise. Much quieter than real drums, but potentially loud enough to bother others. In general, the construction of the floor does not make much of a difference in terms of the loudness of sound of the sticks hitting the pads. Most of that sound is transmitted through the air.
If you can find an apartment that is a basement apartment and is at the corner of the building, that would be your best bet. Set up the kit in the place of the apartment closest to the corner of the building, farthest from the next door apartments. Close all interior doors in the apartment to reduce sound transmission from room to room. After you move in, try practicing on something like a Saturday afternoon. If you're social, meet your neighbors and ask them if they can hear it and/or what times and days would be least bothersome to them for you to make a moderate amount of noise.
That's about the best you can do.
Neighbors to the sides and above will be something to be sensitive about. With upper neighbors, the weight of flooring materials may quiet things down a lot more than the walls to the sides. If the building is composed of concrete decks for each floor, then the upstairs neighbors will probably be unaware of your playing electronic drums. Safer to not assume, though.
