Where is the proper place to put a vapor barrier in a cold climate?

In cold climates, the vapor drive is from the warm interior to the cold exterior during winter. The vapor retarder/barrier belongs on the warm-in-winter side of the assembly—i.e., behind the interior gypsum, before the framing/insulation—to prevent interior moisture from reaching cold layers where it could condense.

PDD references: Psychrometrics & vapor drive; vapor retarder placement (ASHRAE; IBC/IECC guidance; ARE 5.0 PDD—Thermal & Moisture Protection).