Wo Long: Fallen Dynasty

Available during "Fall of the Corrupted Eunuch" which happens during Part 3, at a recommended level of 29. You can always revisit this area via Travel.

It is advised to take care of most of the enemies in the first area. In order to grab this, you'll want to drop down to the bottom level, go to the far back left room to loot the dungeon keys. You can then use the cells to mantle back up to the top level back to the entrance. Here, use the dungeon keys to talk to the man inside, and exhaust all the dialogue options to unlock it.

You can unlock this during the quest "Fall of the Corrupted Eunuch" where you unlock the companion Cao Cao there is a man in a jail cell you need to free by finding a key.

In Fall of the Corrupted Eunuch you can find a man in the locked jail. You need to find jail keys on the bottom level, left of corrupted flag. Using the keys you can open all jails so you can set him free.
Talk to him multiple times to be sure the achievement is popped. You can also find him the base village and talk to him there. Here's the quick run through the mission, keys location [02:26] and setting npc free.