Here is the full list of all 36 Sniper Elite: Zombie Army 2 (DE) achievements.
Successfully complete All Chapters 4 players on Elite Difficulty
Successfully complete Chapter 5 with 4 players
Kill 5000 enemies
Kill 20 Elites in co-op
Kill 2000 enemy grunts in co-op
Successfully complete Chapter 4 with 4 players
Kill 20 Snipers in co-op
Get at least 20 for 1 explosive kill in 4 player co-op
Successfully complete Chapter 3 with 4 players
Successfully complete Chapter 2 with 4 players
Get at least 15 for 1 explosive kill in 4 player co-op
Get at least 10 for 1 explosive kill in 4 player co-op
Successfully complete Chapter 1 with 4 players
Kick 50 enemies down in co-op
Find and shoot all the bottles of blood
Collect all Gold Bars
Become possessed
Defeat 100 ignited zombies
Defeat 10 Fire Demons
Defeat 20 Summoners
Kill 100 skeletons with explosives
Defeat the Final Boss
Kill the trapped Elite
Loot an Elite's corpse
Pick up a phone
Kill a suicide grunt by hitting his grenade
Defeat 500 enemies with headshots
Kill 1000 enemies
Kill any 100 enemy with the shotgun
Defeat a Fire Demon
Kill 500 enemy grunts
Pick up a shotgun
Get a 5-for-1 kill with any sniper rifle
Kill 20 enemies as they revive
Pick up the Preacher
Own 2 Nazi Zombie Army games