Juwon is the "I will confront the other person and not so subtly threaten their entire way of life AND I will sulk for hours and be passive aggressive as hell until you figure out what's wrong" kind of jealous. Followed by the obligatory: "And then I will have a nervous breakdown about my unforgivable inappropriate behaviour, because I didn't mean to infer that you're some kind of possession of mine, and even less that I don't trust you" (until Dong Sik of course takes him out of his misery with a honest chuckle and a promising "It was kind of sexy, though, Juwon-ah.")
Dong Sik is only smiling at the other person - either menacingly or genuinely, depending on the situation. You bet he is protective if necessary; but he never gets jealous - Juwon deserves all the love in the world to start with.
(based on this awesome TDJ gahan post)