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