The motor brushes are located on the rotating armature of the motor.

Look for the large dark gray metal housing in the center of the body of the drill, this is the motor.

The armature of the motor by finding the chuck and the transfer gears, and then look at the other end of the motor. There is a small copper barrel (armature) that is likely colored dark gray from the carbon brushes rubbing against the armature.

On the top and bottom of the armature (small copper barrel), there are brass spring-loaded brackets holding blocks of carbon against the armature; these blocks are the motor brushes.