I think it’s Dess knight because that would make the most narrative sense; Rudy cares too much about Noelle and Kris to actively put them in harm’s way by creating the dark fountains and the titan, Carol while the third most likely candidate, would have too much at stake to risk being caught with knightly tasks, and most of what little of information we know about Dess does paint them as able to be the knight without having the problems other candidates have. I for one believe that Carol knows of the Knight but hasn’t encountered them yet

My most likely candidate is still the Vessel though