An appositive is a noun phrase whereby one noun or in some other cases a pronoun is used, then there'll be another word that'll be used to clarify the noun or pronoun.
In thus case, the noun is "Dr. Benton Jones" while "a winner of the Nobel Prize for his chemistry theories" is clarifying Dr Benton Jones.
Ben is Willy's adventurous and lucky older brother. Of course, he's dead, so he only appears in the play as a character in Willy's troubled imagination. Willy totally idolizes Ben because he was an adventurer who escaped the world of business and got rich quick by finding diamonds in the African jungle
