In my C3 if I rest my thumb on either the temp up/down buttons (but not actually pressing them) on the steering wheel the dash display will quickly change to the inside/outside temp. Let my finger off and it will go back to whatever screen i was on previously. All C models have the screen and the steering wheel controls so I assume it should work in the C2 as well.
I concur, on the Prius c2, the outside temperature is displayed at the bottom of the Drive Information screen only. It is not accessed in any other manner on the C2. Deb
It's one of my very few complaints about the display in mine. Seems like something they could have snuck into the corner of all of the displays, but oh well. I never have a burning need to know the temp, and when I do I can briefly change the display.