What percent of people in Korea do martial arts?

No, of course not. This is a "stereotype"-- when you generalize about all members of a group, even though people in that group might be very different. While some Asians study Martial Arts, it is not a requirement for every Asian, and many Asians never study them. Further, "Asian" can refer to people who are Chinese, Japanese, Korean, Vietnamese, Cambodian, etc.

Certainly, some Asians have become Excellent at Martial Arts, and the popularity of Asian movie stars like Bruce Lee or Jackie Chan may give Americans the idea that all Asian men are masters of kung fu and karate. But in reality, Asian people are actually very diverse, and they have many different interests and many different cultural pursuits.