Temperature of airflow over the wing
I'm extrapolating from general aerodynamics, not asserting a certain answer, but I would expect the airflow across the surface of the wing to be cooler than ambient for a subsonic aircraft.
At the leading edge of the wing, there may be a degree of compression taking place, leading to a small rise of temperature (as there is when the airflow hits the nose of the aircraft, the pitot tube, the air temperatuer probe, and anything else that sticks out). But, as we all know, lift is caused by the reduced air pressure of the airflow as it accelerates across the wing - since the air adjacent to the wing is at a lower pressure than ambient air, I would expect there to be a corresponding cooling effect.
The extent of the cooling (relative to ambient) will depend on the wing geometry, and also on the speed - as you go faster the effects of friction will counteract the effects of the pressure drop, and I suspect that in supersonic aircraft the net result is a warming of the wing skin.
Comments anyone?