"¿Qué puede comer él en ese restaurante?"
Translation:What can he eat at that restaurant?
I agree; It's sometimes tough to know what the subject is. Here is a link about Spanish word order.
the subtle difference: what can he eat in that restaurant? what tastes really good? he can eat everything, because all meals are great. what is he able to eat in that restaurant? please think of his allergy! he is not able to eat everything, because half of the meals contain nuts.