Old Card Game Starting with "SK": It's Almost Certainly Skat

The most likely answer is Skat (not "Skunk"—that's a dice game).

Skat

• Origin: Germany, ~1810–1820; national game of Germany.
• Players: 3 (2 active, 1 sits out each hand as dealer).
• Deck: 32 cards (7–A in each suit; French or German suits).
• Type: Trick-taking with bidding; declarer vs. two defenders.
• Key mechanic: Bid to become declarer, pick up 2-card "skat," choose trump, play alone against both opponents.
• Scoring: Complex; game values × multipliers (matadors, hand, schneider, schwarz).

Other "SK" Card Games

• Skwitz / Scwitz – Scandinavian fishing game (capture cards by matching).
• Schnapsen – 2-player Austrian game; 20-card deck; close relative of 66.
• Skull – Modern bluffing game (2011); coasters, not traditional.
• Skip-Bo – Commercial sequencing game (1967); Mattel.

If None Match

Provide more clues:

• Number of players
• Deck type (standard, stripped, special)
• Trick-taking? Shedding? Matching? Betting?
• Region/country of origin
• Approximate era

Skat is the only historically major "SK" card game. It's deep, competitive, and still widely played in Germany and online (e.g., Skatstube, GameTwist).