The Doctor - S2-E5
Continuity mistake: When Hook is tied to the tree, Emma raises her right hand to her mouth to whistle for the ogres. In the next shot, she uses her left hand. (00:26:45)
The Doctor - S2-E5
Continuity mistake: When Regina is in the stable with Daniel, after she says "No, I won't lose you again", in some shot, she has her hands on his face/neck. In others, her hands are on his shoulders. (00:31:45)
The Doctor - S2-E5
Continuity mistake: When Hook is tied to the tree, the arrangement of the ropes changes throughout the scene. (00:24:40)
The Doctor - S2-E5
Continuity mistake: When the women find Hook under a pile of dead refugees, the amount and position of the dirt on his face changes a couple of times. The scarf around his neck also changes position. (00:01:40)
The Doctor - S2-E5
Continuity mistake: When Emma is questioning Hook while the group is gathered around the bench, the folds in the cloth/bundle lying on the bench keep changing between shots. (00:14:30)
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.