Birth abroad to USC father


I am helping a Puerto Rican friend who was going to med school in the Dominican Republic and had a son with a Dominican citizen woman out of wed lock. He is now in the US and the son is 13 years old. What are the steps in order for him to get him a passport so he can come visit his father anytime. He lived in the US over 5 years before the birth of the child and filed a DR birth certificate there but did not request a US birth certificate. He has pictures with the child and money transfers receipts.