please check out Korean consulate web site before you, there is a pretty accurate guide lines for the process. and yes you supposed to get your diploma notarized from public notary before you get them notarized from Korean consulate.
According to EPIK application guideline, every new candidate must obtain a new set of required documents including criminal clearances as well as a copy of the BA diploma (Apostille attached). EPIK will not accept any documents transferred from ...