The "door" is always on the axis (the imaginary line the station spins on), and it's always the end that turns anti-clockwise.
If you select the station as a target on your display, it'll show the "door" on the hologram.
The "door" always has illuminated billboards outside it, and there'll be more "traffic" on that end of the station that'll show up on your scanner.
If you're approaching the station from the "side" and it appears to be rotating downwards, turn to your right to find the door. If it's rotating upwards, turn left.