Here is the full list of all 36 Sniper Elite: Nazi Zombie Army 2 achievements.
Defeat 20 Summoners
Kill 20 Elites in co-op
Defeat 10 Fire Demons
Get at least 20 for 1 explosive kill in 4 player co-op
Kill 20 Snipers in co-op
Kill 2000 enemy grunts in co-op
Successfully complete Chapter 5 with 4 players
Successfully complete All Chapters 4 players on Elite Difficulty
Kill 5000 enemies
Successfully complete Chapter 4 with 4 players
Successfully complete Chapter 3 with 4 players
Successfully complete Chapter 2 with 4 players
Successfully complete Chapter 1 with 4 players
Kick 50 enemies down in co-op
Get at least 15 for 1 explosive kill in 4 player co-op
Get at least 10 for 1 explosive kill in 4 player co-op
Kill a suicide grunt by hitting his grenade
Defeat the Final Boss
Collect all Gold Bars
Find and shoot all the bottles of blood
Kill the trapped Elite
Kill 100 skeletons with explosives
Loot an Elite's corpse
Defeat 100 ignited zombies
Defeat 500 enemies with headshots
Pick up a phone
Defeat a Fire Demon
Kill 1000 enemies
Kill any 100 enemy with the shotgun
Pick up the Preacher
Get a 5-for-1 kill with any sniper rifle
Kill 500 enemy grunts
Kill 20 enemies as they revive
Own 2 Nazi Zombie Army games
Become possessed
Pick up a shotgun