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