How do you say which extracurricular activities in Spanish?

The most straightforward way to say "which extracurricular activities" in Spanish is:

¿Qué actividades extracurriculares?

You could also use:

* ¿Cuáles actividades extracurriculares? (This uses "cuáles," which is a more formal and slightly more emphatic version of "qué.")

The best choice depends on the context. "¿Qué actividades extracurriculares?" is perfectly acceptable in most situations.