He’s underneath Troika restaurant. Eleventh and 44th.
The boy who was kidnapped in episode 1 was taken to an undisclosed location until Matt beat it out of one of the mobsters. Matt discovers the boy is being held under the Troika restaurant, at 11th & 44th, according to the dialogue on the show. No such restaurant exists at that location, nor were any exteriors of this location shown. Later in the season, this location is one of the four bombing locations Fisk used to eliminate the Russians.
The hallway set below is the only evidence of the location, which was all constructed on a soundstage for the almost five-minute fight scene.
(Daredevil S01E02, 2015)
MCU: Location Scout 