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