It should just show a "cloud" around the screen and you'll see whatever your target sees (ie: censors see Raz as germs, Spy vs Spy agents will see whatever
you're holding's corresponding job).
You'll need to use clairvoyance on a camera in order to see where you're going when in the post office.
Also, more importantly,
you have to use clairvoyance on the helicopter helmet in order for the phone to appear. Then, you can climb the telephone poles and get to the other side.