They wanted Jesus to say something wrong so that they could accuse him. The scribes and Pharisees were trying to trap Jesus so they could accuse him of breaking the law of God, not asking questions so they could learn from him or to convince him that they were right. (See: [[rc://en/ta/man/jit/figs-metaphor]])
The writer speaks of the Pharisees as if they were thieves hiding by the side of a road waiting for someone to come by whom they could overpower and rob. In this case, they were waiting for him to say something for which they could accuse him. Alternate translation: "plotting against him" (See: [[rc://en/ta/man/jit/figs-metaphor]])
The words "something out of his mouth" refer to his words. It is as if the Pharisees were waiting for a physical object to come out of Jesus's mouth so they could catch it and use it as evidence that Jesus was evil. Alternate translation: "him to see if he would say something for which they could accuse him"