hey I'm on the part where you need to found out who is the real doll and I got a question does it have a pattern or is it random?
It took me a bit to figure this out, but the real Sucky shakes a little bit in an upward/downward breathing motion. You should have enough time to find and walk over to Sucky in the time frame the game gives you.
In my experience, you can't find Sucky during the dialogue scenes. However, Sucky is most commonly on the right side of the doll army (again, in my experience).