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