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