The quest can be activated when you enter the Loc Muinne at the beginning of the third chapter, and can be completed immediately.
To find the quest-giver, after you enter Loc Muinne, search the northern camp, near the gate.
In one of the demolished buildings you should see four poker players and Silgrat (A Score to Settle side-quest).
Talk to Filly and Aylaya and win a dice-poker game against one of them.
“Who would have thought that gambling would flourish in the ruins of Loc Muinne? But it Did! Geralt found partners for games of dice poker in one of the ruined buildings, a pair of elves, a sorcerer, his apprentice and a fallen warlock.
Two elves and three magicians make a full house. The witcher decided it was a good omen and dove into gambling. First he had a game with the elves.”
When to start
The quest follows the same rules as the previous tournaments you have won in Flotsam and Vergen.
First, defeat Filly, then Aylaya, then look around for two additional competitors, seating at a table nearby: Hadrian the Black and Adelina. Defeat them too, then look for Incredible Lockhart in the central area of Loc Muinne.
If you beat him, you will complete Poker Face: Loc Muinne.