Since laser uses light, when officers are using laser guns, they're going to want to target the most reflective spots on your vehicle including the headlights, front grill, and front plate (if applicable).
Modern laser guns can get a reading off of most any part of the car and any color car, but those are the general targets they're typically aiming for.
If officers are targeting the rear of your vehicle, it'll be the same areas: tail lights or rear license plate.