What is the correct action for worshippers when the Imam recites tasbih and glorifies Allah during Qunut in Witr or Fajr prayer: Do they say "Subhanak" (Glory be to You) or do they remain silent?

The fundamental principle is that the worshipper (ma'mum) says "Amin" to the Imam's supplication. The meaning of "Amin," according to most scholars, is: "O Allah, answer us." The Shafi'is hold that the Imam recites the Qunut supplication aloud in the Fajr prayer after rising from bowing (ruku'), and the worshipper says "Amin" to the five phrases of the supplication. Then, the worshipper joins the Imam in glorification silently by saying: "Indeed, You decree and none decrees over You..." It is permissible for him to remain silent during the glorification. However, it is preferable to participate in the glorification because it is a form of remembrance that is not suited for saying "Amin." In summary, the worshipper says "Amin" during the supplication and joins the Imam in glorification, or remains silent during it.