hi,

what is the proceeding if somebody from ghana, africa, got the visa
for the wikimania denied at the us embassy in accra?

Not a lot. Embassy are at their discretion to reject anyone they want. Depending on the country, they do usually cite a reason, or hand some rejection letter with an abstract reasoning. There used to be a process to challenge that, but it differs from country to country and is usually quite lengthy, and legal.

Re-application too, might not change much. Unless, the exact reason for the rejection are addressed, perhaps more documents, or support provided by sponsors. But at this stage, it might be too late.

Regards
Theo