Snow Drifts - S3-E21
Audio problem: As past Hook carries Emma aboard his ship, he drunkenly and loudly declares, "Behold! The Rolly Joger." Although they are several meters away from the camera, you can see that his lips are barely moving. (00:32:15)
Snow Drifts - S3-E21
Continuity mistake: Aboard The Jolly Roger, when Emma is keeping past Hook occupied while future Hook skulks around the room, in a wide shot, future Hook sneaks past a corner. In the next shot, he begins to sneak past the very same corner again.
Snow Drifts - S3-E21
Continuity mistake: When Emma is making out with past Hook while future Hook skulks around the room attempting to stay hidden, in the second shot, Emma's back is facing the stairs/ladder, her hand gripping Hook's coat. In the next shot, her back is facing the table, and her hand is on Hook's shoulder. (00:33:20)
Snow Drifts - S3-E21
Continuity mistake: While Henry and his family are gathered around the table at Granny's, the amount of juice in the glass sitting on the table keeps rising and falling. (00:06:50)
Snow Drifts - S3-E21
Continuity mistake: At the docks, when past Hook lifts Emma up, as he says, "Oh, no need", Emma is on her feet, facing him as he begins to pick her up. In the next shot, Emma is facing a different direction, her back leaning against his shoulder/arm as he picks her up and starts carrying her. (00:32:10)
Snow Drifts - S3-E21
Revealing mistake: When future Hook is trying to stay hidden while Emma is making out with past Hook, there is a wide shot where future Hook sneaks past a corner, and you can see the face of Colin O'Donoghue's body double. (00:33:20)
Snow Drifts - S3-E21
Continuity mistake: When Emma changes clothes in the Enchanted Forest, as she puts on gloves, in the wide shot, she begins to put the glove on her left hand. In the following close-up, her left hand is bare, and she's putting the glove on her right hand. (00:18:15)
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.