At the very start of the second mission in the game, Gaberoun, run up and melee kill the guard standing over the red sound contraption that acts to mask your sniper fire. In the distance, there is a man in a tent that is marked as the first objective, but there is also a second guard farther to the left, patrolling outside.
If you stand as far back on the ridge as possible, this guard is over 100 metres away when he stands and faces you, making the testicle shot very easy. Use Focus Time, and wait for the reticule to shrink and aim directly at the soldier’s crotch, slightly to the left or right (gross, I know, but think of the Achievement/Trophy).
If you fail to get the X-Ray kill, restart the mission and you’ll be a mere few seconds away from attempting the shot again. Take a look at the video below to see how we did it: