Jouzu is often written using Japanese kanji. Jouzu is usually used in the sense of “skillful” when “yoku” can mean either “well” or “often” depending on the context. jouzu – 上手 (じょうず) : a but often used as an adjective to mean 'skillful' or 'good (at)' in Japanese. So the 1st sentence is "Your Japanese is great" or some variant. nihongo ga jouzu desu ne. のがじょうず (no ga jouzu) is specific to skills, which can be anything from speaking Japanese to singing like Celine Dion (please don't).