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