South Korean nationals do not need visas for short stays (max. 90 days per 6-month period) in France, in the Schengen area, and in the French overseas territories.
Nevertheless, if the purpose of their stay is to have a professional activity generating a salary, i.e. an activity requiring a work authorization, they need to obtain such an authorization before entering France. (The authorization is asked by the employer to the DIRECCTE).
To check if you should apply for a visa before going to France, please read this page of information.
Some nationalities also need a visa for an airport transit. To check if you should apply for such a visa, please consult this page.