How would you answer yo hago ejercicio hoy?

To respond to "¿Hago ejercicio hoy?" you could say, "Sí, deberías hacer ejercicio hoy para mantenerte saludable," which means "Yes, you should exercise today to stay healthy." Alternatively, if you want to suggest a specific time, you might say, "Podrías hacerlo por la tarde," meaning "You could do it in the afternoon."