I’m in AP Spanish IV for Native Speakers and I believe it’s Tocar but in the sentence it would be Toco since it’s conjugated. It would say “Yo toco el piano”, “I play the piano”. Escuchar wouldn’t make sense because it would say “I listen the piano.” Hablar wouldn’t either because you can’t talk to the piano and hablar means to speak. Also, estudiar (which someone said is the correct answer but isn’t) doesn’t make sense because you can’t study a piano. You can study how to play a piano but not the piano itself. The whole study things just sounds weird. Tocar/Toco makes much more sense. I hope I helped! (:
