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