Movie About a Genius Who Wins at Gambling: '21' (2008)

You're likely thinking of 21 (2008), based on the true story of the MIT Blackjack Team.

• Plot: Math prodigy Ben Campbell (Jim Sturgess) joins professor Micky Rosa (Kevin Spacey) & team counting cards in Vegas.
• Not a game show: It's casino blackjack, not a quiz show.
• Similar vibe: Quiz Show (1994) – 1950s quiz show scandal; Slumdog Millionaire (2008) – game show Who Wants to Be a Millionaire frame story.

If it's a different film, share details (era, tone, specific scenes).