Here is the full list of all 36 Sniper Elite: Nazi Zombie Army 2 achievements.
Kill 5000 enemies
Collect all Gold Bars
Get a 5-for-1 kill with any sniper rifle
Kill any 100 enemy with the shotgun
Find and shoot all the bottles of blood
Defeat 20 Summoners
Defeat 100 ignited zombies
Kill 100 skeletons with explosives
Defeat the Final Boss
Kill 20 Snipers in co-op
Kill 20 Elites in co-op
Successfully complete Chapter 5 with 4 players
Successfully complete All Chapters 4 players on Elite Difficulty
Kill 2000 enemy grunts in co-op
Kill 20 enemies as they revive
Successfully complete Chapter 4 with 4 players
Defeat 10 Fire Demons
Get at least 20 for 1 explosive kill in 4 player co-op
Kick 50 enemies down in co-op
Get at least 15 for 1 explosive kill in 4 player co-op
Kill a suicide grunt by hitting his grenade
Defeat 500 enemies with headshots
Kill 1000 enemies
Successfully complete Chapter 1 with 4 players
Become possessed
Own 2 Nazi Zombie Army games
Loot an Elite's corpse
Kill the trapped Elite
Pick up the Preacher
Kill 500 enemy grunts
Successfully complete Chapter 3 with 4 players
Pick up a phone
Pick up a shotgun
Successfully complete Chapter 2 with 4 players
Defeat a Fire Demon
Get at least 10 for 1 explosive kill in 4 player co-op