What is the best way to get to Debrovnik from JFK and return via Split to JFK? Other recommendations for different East Coast airports? Thanks
You'll probably connect in Europe.
Depends on the time of year. I believe there is a direct from Newark to Dubrovnik in the summer. Otherwise you will need to have at least one connection in Europe.
Here I made some searches on Skyscanner for eg. in January. You can compare the prices of Skyscanner and Google Flights.