Continuity mistake: When Emma hears the scream and asks Ruby what's going on, her hands are bare, but as she runs off to investigate, she's suddenly wearing red gloves. In the next shot, her hands are bare again. (00:40:30)
Continuity mistake: Regina and Daniel are in the stable. Regina's hands are on his face, he reaches up and pulls them down, cut to behind Daniel and her hands are back up on the side of his head. Cut back to side view, and Daniel's hands are still holding Regina's down. (00:16:40)
Continuity mistake: Regina is talking to a young Snow White about how her love ran away. Her lipstick goes from a bright pink to a brownish red when the shot changes angles, and stays that way the rest of the scene.
Continuity mistake: When Regina is standing by the tree with Daniel, as she says "Have you not seen her magic?" Rocinante, Regina's beloved horse, is standing next to them. In the following wideshot, Rocinante is nowhere to be seen, and there was not enough time to move away from them. (00:08:05)
Continuity mistake: When Regina first kisses Daniel, her head is tilted to the left. In the next shot, her head is tilted to the right. (00:05:05)
Character mistake: In the newspaper article that Emma reads, Kathryn Nolan's first name is misspelled "Katherine." (00:19:45)
Answer: He knows who she is because he knows that the fairy tales are true. He was also shown to sneak out to go see Emma or someone else. Sometimes he succeeded, sometimes he didn't. This is how he knew to look for her despite his strict mother.