What does "Who knows" mean in English for Spanish?

In English for Spanish, "Who knows" means:

¿Quién sabe?

Listen to "Who knows": (If you have an HTML5 enabled browser, you can listen to the native audio below)

This is a phrase that is used in the GamesForLanguage English for Spanish Language Game in the following scenes:

• English for Spanish 4, Level 3, Scene 6