Mountain Temple - Ambush Inside the Burning Building - Part 1

Sneak through the passageway. As you approach the first soldier, the game explains how to do a stealth kill: Sneak up on an enemy whose back is turned and when you see the Melee icon, press that button (F/Triangle/Y) to get the guy in a choke hold with your bow.

Then tap the Interact button, as shown on screen, to finish him off. Notice how you gain bonus XP for a stealth kill.

Now immediately turn left and take out the second man using a headshot before he can alert more enemies.

There's a lantern (4/5) on the other side of the room near some flammable cloth. I'd recommend you don't shoot it. It does count toward the challenge, but it also alerts all the enemies in the area, making it much harder to get out alive. There are other lanterns later on, so it's OK to skip this one.

Carefully loot the 2 bodies as you move behind the farthest crate ahead on the right.

Stay here under cover and look up to the right, where more enemies are moving around with flashlights. If you activate Survival Instinct you'll notice some enemies glow red instead of plain white. This means they will alert other enemies if they're shot. So avoid targeting anyone who glows red.

Wait until the guy on the right moves off, leaving the guy on the left alone. Then target him with a headshot.

When the other guy comes back, try and get him with a headshot as well.