If I was asked that question, I would refer the person to the Catechism, the Code of Canon Law, and the teachings of the whole of the twenty-one ecumenical councils, and also a peppering of significant papal documents from throughout the ages.
I am simply dispelling your ridiculous assertion that Vatican II “contains all the answers” or something. Truth be told, most Catholic teaching was the same before Vatican II was ever dreamed of. It added to Catholic teaching, to be sure, but it did not wipe everything clean and start over. I mean, if it did, the documents of the Council wouldn’t have quoted from other documents of other councils, would it?