Term (phrase or word) for action to take as a penalty for losing a bet (or a game, etc.)

Solution 1:

Consider forfeit, that is given up or performed by the player losing the game or committing a fault.

In your first example, the second sentence would be "What forfeit will you pay ?".

Example: Jamie Carragher (Liverpool FC) has agreed to suffer the forfeit of wearing a Manchester United shirt after losing a bet with Gary Neville that relates to Tottenham midfielder Paulinho.

Solution 2:

It's a stake, of the not vampire-stabbing sort.

stake NOUN A sum of money or something else of value gambled on the outcome of a risky game or venture - ODO

figurative the opposition raised the stakes in the battle for power