Bear in mind the following info is 2 years old...but here it goes:
KAL fly you on their network to INC in business class. You stay at the Hyatt INC which is very comfortable with a gym and a few restaurants with a variety of food types. There is a crew room in the hotel where you can get free internet.
Upon check-in you will get a package identifying who your sim partner will be as well as your program for your assessment along with bus tickets and instructions in Korean for taxi drivers to get you where you need to go.
The sim assessment is basic and was conducted by a Korean instructor. You will be well briefed and there are no tricks, just fly and do what you are told.
The interview is basic also...the key being to speak SLOW and ANNUNCIATE your words. They want to see that your English is of a high standard and that you will be understood by your companion in the flight deck. There were no technical questions, just the usual why do you want to work there etc. It was a panel of about 6 or 7 if I remember although only 2 or 3 asked questions. The interview lasted about 15-20 minutes.
The medical is intense, and takes a whole day with part done at the HQ and part at a local hospital. On a personal note, while I found the medical quite intrusive, to their credit they discovered a life threatening problem which my family GP had never discovered and frankly I am alive today because of that medical.
The whole process took 2 days and is very well organized. You must bear in mind that this is Korea and their culture is not a Western one and they do things differently. I was fortunate to be involved in an audit on KAL in 1999 when they had a bad rap for crashing airplanes and can testify that KAL have the will, the money, and the people to make KAL into a world class airline. There were bad apples in the mix but they are becoming rarer. Again, it isn't a Western culture, and their ways may seem alien, so if you can get your head around that you should fit in nicely.
Good luck.