He would first have to take a taxi to the bus terminal in Fruisa which is about 15-20 minutes. It is where Expreso Bavaro is, but he needs the bus to Higuey on his right looking at the ticket counter. Any taxi would know this.
Then he takes the bus to Higuey about 50 minutes. At Higuey he changes to a bus to SD. It is close to where he lands in Higuey. This bus will stop in Juan Dolio. This is the ONLY way to get there without taking a taxi all the way.
Also he cannot take the Expreso Bavaro bus because it will not stop in Juan Dolio and he would end up in SD.