I have tested your source by installing NotoSansCJKkr-Regular.otf etc. It seems to work OK. Note that I'm using ".otf" fonts, not ".ttf" ones. I attach cjkkrtest.tar.gz in which there are k.tex and k.pdf.
Your output is perfect. But I still get an error message which is as same as Luigi mentioned. Would you please send K.log file to compare with mine?
luatex crashes with error message mtx-context | fatal error: no return code, message: latex: execution interrupted
Under WINE (linux) mingw 64bit, luatex.exe Version beta-0.79.1 (TeX Live 2014/W32TeX) (rev 5041) is ok
luatex.exe experimental is also also ok and both give the same result of u.pdf
My version of latex is This is LuaTeX, Version beta-0.79.1 (TeX Live 2014/dev) (rev 4972) But it is not ok for me. Anyway, there is some problem in my TeX system rather than in the font. I’ll check it. I am using ConTeXt standalone in Mac Maveric. Thank you. Best regards, Dalyoung