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