to do this you need to find Cale in the forest of the fallen giants and exhaust all of his dialogue. You will get a key that unlocks the manor in Majula, go there and kill the monsters in the basement.
Then you need to complete every major objective for the story completion.
After watching the ending cutscene you can return to the manor. Find cale in the basement and Again talk to him and exhaust all of his dialogue to pop the trophy and get some swag poison resist gear.