Final answer:
The verb that fills in the blank is 'juegas'.
Step-by-step explanation:
The verb that fills in the blank in the sentence 'tú jugar al tenis?' is juegas. The correct sentence would be '¿juegas tú al tenis?'. In Spanish, the verb forms change depending on the subject. 'Tú' is the subject in this sentence, so we use the verb form 'juegas', which is the second person singular form of the verb 'jugar' (to play).
Learn more about Spanish verb conjugation