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