This locker, measuring 12.5" x 22.75" x 4.75" (at top- tapering to 2,25" at bottom) would mount in the upper section of the command module, above and behind the heads of the astronauts.
This particular design was made for the later "Apollo Applications" missions (Skylab and Apollo-Soyuz Test Project). The markings on the inside of the bi-fold door includes a part number "V56-331540" and "UNIT-119", signifying that this particular locker had been installed in Apollo CSM-119, which was the flight-ready rescue vehicle for the Skylab missions and backup craft for the ASTP (which is now on display at the Kennedy Space Center).
Note how the tapering maximizes the available space, with the locker shape following the spacecraft contours.
According to NASA documents, during a typical mission, stowage locker U4 contained “4 cassettes, 4 batteries for tape recorders, a 10 x 40 monocular, an intervalometer (Hasselblad), and a 250mm lens.”