how a ghanaian staying in china as student can get holidays visa to go south korea.

You can choose the right place to apply for your visa to South Korea according to the consular divisions on this page: https://www.travelchinaguide.com/embassy/foreign/beijing/korea.htm

As I know, the Embassy & Consulates of South Korea in China have their appointed travel agencies for the visa service. You should contact the exact embassy or consulate where you should apply for the visa to know the name list of the authorized travel agencies.

If you will go to South Korea for sightseeing, you will have to prepare the visa appliccation form that should be completely filled, you passport, your residence permit in China, financial proof of adequate funds for your duration in South Korea and a recent-taken passport standard photo.