From Abidjan, the most reliable option is the STB coach service from Treichville — the journey takes around eight hours. Several other coach operators also run the route, including UTB and SABE Transport.
Ivoir Airways used to operate flights from Abidjan to Bondoukou, but service has been intermittent; check current schedules before counting on it.
From the east, Bondoukou is reachable from Kumasi in Ghana via the border crossing at Sampa. The road is paved on the Ghanaian side; expect rougher conditions once you cross into Côte d'Ivoire.