Answer:
Perdone señor, ¿Cuándo sale el tren a Barcelona?
Explanation:
Present Simple of salir:
Yo salgo
Tu sales
Él/Ella sale
Nosotros salimos
Vosotros salís
Ellos/Ellas salimos
"El tren" (the train) is the 3rd singular person, thus the correct present simple verb form of "salir" is sale.
Another little thing, there was a typo in your question. It's not "perdoñe" but "perdone".
Native speaker over here. I hope this is helpful.
