The first place you should contact is probably the Korea Office of Civil Aviation:
KOCA
They will know what your partner needs to do to get a Korean flying license.
If there aren't any schools in Korea that your partner wants to train at then the quickest and cheapest way to get a commercial pilots license is to go to USA. A google search will give hundreds if not thousands of options for flight training across USA and the rest of the world. It's possible to start his training for a Private Pilot License and continue in stages to get the Commercial License later.
If he completes his training overseas then he will gain a flying license from the country he is training in. Again the Korea Office of Civil Aviation will know how to convert this into a Korean license.
I have met a couple of Korean pilots flying as expats in Asia. One of these started his career in another country so it is possible.
As you've probably guessed by now, one golden rule of flying training is NEVER pay the whole cost up front.
Good luck.
P.S. Your english is excellent.