"Tu ne sais plus qui c'est ?"
Translation:You don't know who he is anymore?
It is my understanding that there is NO difference in pronunciation. Or if there is, it varies by region. At least c'est is never preceded by a subject (je c'est, tu c'est...) As it just makes no sense. C'est already contains the subject. You WILL hear sais/sait preceded by a subject.