WIth a gazillion Japanese who can pass for Korean, and vice versa, (for a variety of reasons going back millenia), not sure that question is meaningful.
Modern Koreans probably have a bit more Tibetan in their lines than the Japanese, and less Jomon, but they both have a touch of Hakka, and unless you have the really flat Moon face look, that's a pretty dominant "face" in both countries ~ except among the Emishi and Ainu.
Hard to stick out in that crowd!
Unless they were born and raised in Japan as a zainichichosenjin, then they are liable to be discovered once they talk.
It starts with the very Korean accented "arigado-gojaimaz" way of saying thank you that alerts a true Japanese they are not Japanese. When I heard spy Kim Hyun Hi (the DPRK female bomber of the KAL flight sent out by Kim Jong il to do the deed) after she was captured and interviewed for Japanese TV, I can see how she maybe passed herself off as a Japanese when caught be Dubai authorities, but if I were in that room I would have known she was Korean in five seconds. It was when the Japanese authorities arrived to talk to her that they got it right away. Very very think Korean accent. Other than that, physical characteristics can be about the same. Give them a "Hello Kitty" bag and it will work for awhile I suppose.
I did in Shinjuku, but the closest I get to Jomon is Chactaw :)