This is one of the RNG based achievement
In this game, you are exiled , so did Rogue Exile.
You, as the playable character, will randomly encounter Rogue Exile in the whole game, which they are hostile NPC. You can wait the dev to organize event that enable Rogue Exile forced spawn modifier in this area: Kaom's Stronghold.
However, tedious but effective way to do it, is keep grind this area, carpet clearing all monster (or have a very good eye to spot the Rogue Exile) until you have this achievement
Each Rogue Exile has its own name and skill
Here is the incomplete list
https://www.poewiki.net/wiki/Rogue_exile