The pair are together this month at the U21 Euros, having also worked together inside the Chelsea academy.
"He was in the under-21s, in the reserve group at Chelsea," said Cole in Slovakia. "You always see the passion and level he could get to.
"I think him getting the opportunity at Newcastle and continuing to play first-team football gave him the belief, the confidence in his own ability.
"And of course, a manager that's trusted him to play at such a young age. I think he had quite a big challenge going to Newcastle, but he's developing into a top player."
Eager to learn
Cole also said: "As a coach, you stand on the sideline and see how much information he takes on board.
"And I keep saying it, but the willingness to want to learn and be the best, I think is always a great trait to have.
"Whatever level he wants to get to, he can get to because he's got that personality and desire.
"I think he's got a beautiful future, a bright future. Long may it continue that he keeps playing for Newcastle, keeps gaining experience and keeps his levels up."