Here is the full list of all 36 Sniper Elite: Nazi Zombie Army 2 achievements.
Defeat 20 Summoners
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
Defeat the Final Boss
Get at least 20 for 1 explosive kill in 4 player co-op
Kill 5000 enemies
Successfully complete Chapter 4 with 4 players
Successfully complete Chapter 3 with 4 players
Successfully complete Chapter 2 with 4 players
Kill 20 Elites in co-op
Kill 100 skeletons with explosives
Find and shoot all the bottles of blood
Collect all Gold Bars
Defeat 10 Fire Demons
Kill any 100 enemy with the shotgun
Pick up the Preacher
Kill the trapped Elite
Kill 20 Snipers in co-op
Kill 20 enemies as they revive
Pick up a phone
Kill a suicide grunt by hitting his grenade
Defeat 100 ignited zombies
Kill 2000 enemy grunts in co-op
Kick 50 enemies down in co-op
Defeat 500 enemies with headshots
Get at least 15 for 1 explosive kill in 4 player co-op
Successfully complete Chapter 1 with 4 players
Become possessed
Kill 1000 enemies
Get at least 10 for 1 explosive kill in 4 player co-op
Kill 500 enemy grunts
Defeat a Fire Demon
Loot an Elite's corpse
Pick up a shotgun
Own 2 Nazi Zombie Army games