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