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