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