This is the root of a Chinese Bellflower species used extensively in Asia for its herbal properties. Known as 'doraji' in Korea, it is sold either dried or fresh, and is widely used in salads and traditional herbal cooking.
The dried product requires extensive preparation to strip it of its chemical taste - soak it overnight, rinse several time, and boil - and the fresh roots require only slightly less work: substantial scraping and several hours of soaking. Once clean, it does not require much cooking, and can be eaten raw.
Should not be confused with the inedible roots of the Korean bellflower.