The personality trait that would make Dickon feel at home at Buckingham Palace or at the bottom of a coal mine is that he is very likable.
It is mention trough the book that he has a strange ability to captivate everyone human or not since his ability also applies to animals, everywhere Dickon goes everyone just fell under his spell and find him lovable. We can see the quotation that says :
There really was a sort of Magic about Dickon, as Mary always privately believed. When Mr. Roach heard his name he smiled quite leniently.
“He’d be at home in Buckingham Palace or at the bottom of a coal mine,” he said. “And yet it’s not impudence, either. He’s just fine, is that lad.”
