Question

how did Nicola and jacopo prove extremely useful to the narrator

Answer 1

Nicola and Jacopo helped the  narrator in every way they could. They showed him and his friend various places of tourist interest in Verona. Whenever the narrator needed a guide, Nicola and Jacopo were at his service. So, they proved themselves to be extremely beneficial for the narrator.

Answer 2

Nicola and Jacopo were proved extremely useful to the narrator because they both were guided the narrator and his driver to the tourist places, booking tickets for Opera, finding them hotels and many more in the city of Verona.

I hope it will help u. :)