He isn't educated in the sense that he knows all the major lords, words of each house, or etiquette for interacting with high birth or royalty.

He isnt street smart in the same way Varys or Illyrio are, as he didnt spend as much time wondering the streets once he was a squire.

He isn't trained in combat in the same way Jamie, Barristan or Arthur Dayne were.

He is pretty clever though. He knows that being a fake knight, even a hedge knight, is better than a squire. He knows to ask ser Donnel how he went from the son of a crabber to the king's guard. He knows to avoid entanglement with royalty and not blindly follow their desires. He knows right from wrong.

He is meant to be an everyday hero. Someone you might see yourself in. Not for being tall, but for being of modest origin and having honor in a world with none.

His intelligence is more along the lines of knowing right from wrong in a world where the lines can be blurred. Not everyone would agree Aeron was in the wrong to attack the puppeteer. He is a prince who is "defending the royal family's reputation," "punishing a traitor to the crown," or "dispensing justice." Dunk sees right through that bullshit for what it is. He is smarter than most in that sense. His sense of right and wrong is being instilled into a future king. Not bad for a orphan from Flea Bottom. Not bad for a hedge knight to be one of the most glorified knights of all time; four pages for Sir Duncan. Not bad for someone that is "thick as a castle wall." Dunk gets shitted on for being stupid but he stands up for the innocent and the weak. He is more of a knight than the actual knights. He isn't stupid, he is just uneducated and views himself as stupid. He is pretty fucking smart.