When you reach Split, take a ferry to Supetar on the island Brac (1 hour trip). From Supetar, you have to go another 39 km by car/bus/taxi to Bol. You can also reach Bol directly from Split, travelling by catamaran.
You can look up more information on ferry and boat lines and schedules on the web pages of "Jadrolinija".
For everyday bus lines Supetar-Bol check the web pages of "Autotrans Brac".