Learn French: Quand est-ce que tu finis tous les exercices ?

Tous is the masculine plural form of tout (all). It has to match the gender and number of the noun it describes. Because exercice is a masculine word and it is plural here (les exercices), we use tous.

Do I pronounce the "s" at the end of tous in this sentence?

No, the "s" is silent here. When tous is used as an adjective followed by a noun (meaning "all of the..."), you pronounce it like "too". You only pronounce the "s" (like "tooss") when tous is used all by itself as a pronoun, meaning "all of them" or "everyone".

Why do we say Quand est-ce que instead of just Quand?

Est-ce que acts like a question marker. While you could say Quand finis-tu... by swapping the verb and subject, adding est-ce que directly after Quand is very common in everyday spoken French. It lets you keep the normal tu finis (subject + verb) word order.

Is finis an irregular verb?