Jesus refuses to answer the priests' question because they were not bold enough to give their true opinion. They were afraid of the people.
If we are seeking knowledge from Christ, we have to do two things. First, we have to be willing to be wrong. The priests had a wrong idea about John (that he was not from God), but wouldn't share that opinion. If they had, Jesus would have been able to teach them. If we want Christ to teach us, we have to be willing to be wrong. That takes humility.
Second, we need to be bold enough to forget human opinion and focus only on Christ. Again, if the Pharisees were willing to give some answer instead of being intimidated by the crowd, they would have had the opportunity to learn.
To learn from Jesus, approach Him boldly, forgetting others' opinions, and be willing to be corrected. Boldness mixed with humility. Courage mixed with a teachable heart.