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