One of a number of Gwent quests you must complete in order to finish Collect ‘Em All.
The Witcher 3: Gwent: Old Pals
Gwent: Old Pals is one of the trickier of the Gwent quests. Not only do some of the characters become unavailable if you leave it too late (as with most Gwent quests), it can be difficult to track down some of the participants.
The easiest time to kick off this one is at the end of the Broken Flowers quest in Act One: Novigrad. Having completed this quest, you can challenge Zoltan Chivay to Gwent just outside Dandelion’s Thyme and Rosemary inn.
Zoltan gives you a few player leads. The most easily available one is Vernon Roche. Head to the Temerian Partisan Camp to challenge him – if you haven’t been there before, make sure this objective is selected in your quest menu for a waypoint. If Roche is not at the camp, you’ll need to complete An Eye for An Eye, or advance A Deadly Plot to the second objective, or both to make him available for play.
Speaking of A Deadly Plot, you must complete this quest to challenge Thaler, another of your targets. You can either challenge him right after you rescue him from the trolls, concluding the quest, or find him later at the Seven Cats Inn in Novigrad. Don’t worry; completing A Deadly Plot does not commit you to the assassination plan.
The hardest target to pin down is Lambert. You should challenge him during the quest Following the Thread if possible; otherwise, there are unconfirmed reports he will play you at Kaer Morhen in Act Two. He’s very easy to miss so be attentive and follow the linked walkthrough.