Here is the full list of all 38 Sniper: Ghost Warrior 2 achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Take 50 headshots in single player
Rescue the friendly ("From Out Of Nowhere")
Kill 20 enemies from a distance of 600m or greater
Take a successful shot from a distance of 1 km or greater
Complete Act 1
Complete Act 2
Complete the game on Casual
Complete the game on Medium
Complete the game on Expert
Collect all secrets in Act 1
Collect all secrets in Act 2
Collect all secrets in Act 3
Kill three or more enemies by shooting a grenade
Achieve 100% accuracy in any single player mission
Complete any single player mission without using med kits, but taking damage
Kill 30 enemies using your sidearm
Kill 15 enemies with a stealth kill
Kill 50 enemies while holding your breath
Kill 25 enemies using thermal or night vision goggles
Kill Major Vladic ("And Justice For All")
Kill Maddox once and for all ("No Loose Ends")
In the final duel with Maddox, kill him with the first shot ("No Loose Ends")
Kill all enemy snipers in Sniper Alley without being hit ("Ghosts of Sarajevo")
Retrieve your weapon without being detected ("Burning Bridges")
Kill all enemies in the beach houses without causing an alarm ("Leave No Man Behind")
Complete any act without using medkits
Complete the Campaign using max one medkit per mission
Kill 25 opponents in multiplayer
Kill 50 opponents in multiplayer
Kill 100 opponents in multiplayer
Take 25 headshots in multiplayer
Take 50 headshots in multiplayer
Kill 10 opponents in multiplayer using your sidearm
Win 5 rounds in a row in Team Deathmatch
Win 10 Team Deathmatch rounds
Win 25 Team Deathmatch rounds
In one multiplayer round kill an opponent with a sniper rifle, sidearm and melee attack
Participate in any multiplayer match