My friend is an Indonesian and would like to travel to South Korea, he holds a Japan technical intern visa.
Will he be exempt from a South Korean visa? If not, how should I get the South Korea visa?
Per TIMATIC, an Indonesian citizen needs a visa unless they hold a visa for certain other countries1, Japan not included. To obtain a toursim visa (probably B2), the person trying to visit should contact the nearest South Korean embassy.
1 Australia, Austria, Belgium, Canada, Cyprus, Czech Rep., Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland (Rep.), Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Netherlands, New Zealand, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, USA or United Kingdom