kung fu isn't generally my bag, and i'm not sure if it counts as strictly a kung fu movie, but i'll say old boy. it's about a man imprisoned for 15 years, without knowing who his captors are or why he is being held. https://image.tmdb.org/t/p/original/idBaREsAGTjPZPrlAd1w8SVzUzd.jpg

otherwise i'd say the kill bill movies