Upvote:3
For Jeju island, Nigerian and Ghana passport holders need a visa for South Korea.
https://en.wikipedia.org/wiki/Visa_policy_of_South_Korea#Jeju_Island
For the tourism purposes, you are required to apply for B-2-2 for Jeju island in your nearest embassy.
Nigeria: http://overseas.mofa.go.kr/ng-en/index.do Ghana: http://overseas.mofa.go.kr/gh-en/index.do