What should I do if the Imam makes a mistake in a word of a verse during prayer, and I do not remember the correct word; should I alert him by saying "SubhanAllah" or remain silent?

It is prescribed to correct the Imam if he makes a mistake in recitation during prayer. However, it is not obligatory unless the mistake is in Surah Al-Fatihah, or it is a mistake that alters the meaning, in which case correction becomes obligatory. If the Imam makes a mistake and the worshiper does not know the correct recitation, then he should remain silent so as not to cause disruption, and the prayer is valid. If the worshiper knows that his glorification will correct the mistake without causing harm, then it is recommended for him to glorify Allah (say "Subhanallah"), due to the general meaning of the Prophet's (PBUH) saying: "Whoever encounters something (unexpected) during his prayer, let him glorify (Allah)."