The first Place where you can do this, is directly in Chapter 1 called Siege of Tobruk.
After the first 2 Enemies in the Game (Spotters), you go a little forward and third Spotter spawns on the Mountain over 100 Meters away. Create a Savegame before you shot and aim between the Legs. If you miss the Testicles load the Savegame for a new try. The Spotter has now a slightly different Position. I put all 2 Shots in this Video.