If you look back to chapter four, then you'd see that there was a code in Dess's guitar, so she could be it right, but the thing is, that was to the parental code so that Kris can't watch those band videos that Dess put on, so it makes more sense for the mayor to be the knight, the mayor, a pine tree (symbol of the code) Undyne, police badge (symbol of the code) Alvin, Deltarune (symbol of the code) you may be confused about Alvin, but remember what all the chorus girls wear at church? A purple robe with the deltarune on it, who is in charge of the church and most likely chose that? Alvin, so he's not off the hook, but the knight had a sword, almost like a katana, think about it for a second, in chapter 4 the person blocking your way to the mayor says "The mayor destroyed my briefcase with a katana" so Carol's not off the hook either, but we know it's not Susie, Kris, Ralsei, Undyne, or Soulless Kris, because they were all there at the same time as the knight, which also means the same for Torial, but as I'm typing this, I just realized, what about Asreil? We haven't seen him, but then if you think about it, the knight can only be Dess, Carol, Rudy, or Noelle, but since we've seen everyone but Carol, what about the fact that it showed this "the helmet came off" and then it was just talking about Jockington after that, but the knight has reindeer antlers, it shows that everyone but the holidays are clear, but Rudy's clear since he's always in the hospital, and Noelle is clear because she doesn't know what the soul can do, so it leaves Dess and Carol, but since Dess is missing, most likely at collage, Carol is the only one left, and there's no determining otherwise, Carol is the knight