The Sanhedrin's question is for intimidation and ammunition, not information. Jesus's counter-question about John's baptism is a standard rabbinic technique that embeds his answer while denying them usable ammo.

Two purposes behind their question: (1) Intimidation — the Sanhedrin was highly respected (not losers; they were the heroes/celebrities of the day), using authority to pressure Jesus to back down; (2) Ammunition — they wanted Jesus to claim divine authority so they could charge him with blasphemy. Jesus responds with a counter-question (a common rabbinic practice, not evasive): "Was John's baptism from heaven or from men?" This embeds his answer — John's ministry was entirely about pointing to Jesus as Messiah, so affirming John = affirming Jesus's authority. But asking a question denies them courtroom-usable ammunition. Note: Jesus DOES answer plainly in Mark 14:61-62 before the Sanhedrin — it's just that moment leads directly to his crucifixion.