I would just roll total moxie times ten, and have him suffer stress when they lose, which makes them gamble more. On the flip side, i'd let them recover stress along with money/rep when they win. The interest or profession, is for them to find the game they want. And is it a minor or a server addiction? If its the latter, then they're borrowing money and betting money they dont have. From not so legal bank like operations. The bad news is that unlike actual loan sharks they will break your knees and elbows because your body will fix itself and doesnt really stop you from earning money.

Decide the level of abstraction and sci-fi hardness of your gambling. If you want to go low abstraction and soft then play few rounds of blackjack with your player eventually giving him tips based on his "profession/interest: gambling" rolls. The would represent counting cards and other tricks. I recommend checking the interwebs for RPG gambling games. If you want high abstraction, hard sci-fi then give him neopoker which REQUIRES math whiz, mental speed and eidetic memory to even participate is played with 42 decks of cards, players have 15 kinds of action and can communicate freely with themselves in public and in secret. This gives the game ability to be socially engaging and schemes, intrigues etc. flourish. The games are held within faraday cage isolated rooms. It is said that during the fall AGI neopoker players were hunted, by titans for assimilation and/or preventing them from achieving seed AI status. It is a game popular amongst Ultimates, Exhumans and Hyperelite. Neopoker players are automatically banned from "classic" hazard games, but their scene produces a plethora of other lesser games which are the pastimes for between the neopoker matches. EDIT(bonus because I feel inspired): Chess is considered a special ritual where opponents sleeve into identical specially engineered unaugmented splicers or bare infomorphs and compete in the ultimate battle of wits. There is no betting on chess because the game can be staged too easily. Genuine game is sometime two clones staring at each other for hours on end, making few moves and suddenly one player realises he will be defeated in five to ten moves and surrenders. Rigging player simply can surrender without this realisation and later claim that winning was simply beyond his abilities.

Hazard game? Like from the The Culture series?

I think the word you want is "Chance". Hazard and risk both do a better job of communicating the potential for financial loss, but those are not the colloquial words for it. At least not in the States. When you wrote "risk" there, I first thought of the thing by Parker Brothers. Speaking of The Culture, some analogue of Azad would be good for EP, as your tactics reflect your cultural values, the stakes are your Rep. You wouldn't be playing for favors or cash, rather for Rep its self.

Abstraction would be key. It would just be a series of contests over time. Tournaments would span a few days. Casual "pickup" games might be just one of the small mini-games that comprise a traditional tournament, but played by its self. You'd probably pick some sort of skill like tactics, and use knowledge and cultural skills as complimentary. There might be some sort of meta-game behind it, where you build up advantage or "taking your time" bonuses through your actions between the actual tournament rounds. Maybe the primary skill you use is a different "Active Mental" skill determined by each round of the game. You could freely associate your complimentary skills from any of the Knowledge types, with the caveat that you can only use each skill in one round. Maybe you could re-use a skill, at the price of giving your enemy an increasing advantage each time you did it.