If you are booking on KoreanAir.com, it will list the fare class next to the flight information. You can also click on "fare Information" and it will list the class or a list of letters. The class is the first letter.

You can also get it from the customer service center.

I get SkyMiles on my KE flights. They always accumulate (K,E,H,Y,B,M). The only flights that don't are Q class, I believe, and those are the fares that are obviously cheaper. They are more common here in Korea.