Where did David's stone strike Goliath?

Answer: In the forehead

The stone sank into Goliath's forehead, and he fell facedown on the ground.

“Then David reached into his bag, took out a stone, and slung it, striking the Philistine on the forehead. The stone sank into his forehead, and he fell facedown on the ground.”— 1 Samuel 17:49 (BSB)