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