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