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