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.
Win 25 Team Deathmatch rounds
Kill 100 opponents in multiplayer
Take 50 headshots in multiplayer
Win 10 Team Deathmatch rounds
Kill 50 opponents in multiplayer
Kill 30 enemies using your sidearm
Win 5 rounds in a row in Team Deathmatch
Kill 10 opponents in multiplayer using your sidearm
Take 25 headshots in multiplayer
Participate in any multiplayer match
In one multiplayer round kill an opponent with a sniper rifle, sidearm and melee attack
Kill 25 opponents in multiplayer
Collect all secrets in Act 2
Collect all secrets in Act 3
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")
Complete the game on Expert
Complete the game on Casual
Complete the Campaign using max one medkit per mission
Complete the game on Medium
Kill Maddox once and for all ("No Loose Ends")
Retrieve your weapon without being detected ("Burning Bridges")
Complete Act 2
Kill Major Vladic ("And Justice For All")
Kill 15 enemies with a stealth kill
Collect all secrets in Act 1
Complete any single player mission without using med kits, but taking damage
Complete any act without using medkits
Complete Act 1
Kill all enemies in the beach houses without causing an alarm ("Leave No Man Behind")
Kill three or more enemies by shooting a grenade
Kill 25 enemies using thermal or night vision goggles
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
Achieve 100% accuracy in any single player mission
Take 50 headshots in single player
Kill 50 enemies while holding your breath