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With all due respect, this certainly is a noun, defined as “a person, place, or thing” and it is a proper noun and thus deserves its capitalization. (It is also a compound noun.)  There is no argument for its being a pronoun—it stands for a person, real or ficticious, whose name is Ernestine Jones.  Taken out of context, one cannot say it’s a subject, object, etc. because those are parts of a clause structure. If, in a complete thought, the writer/speaker does not want to repeat the name, a pronoun can replace it (example: “Ernestine Jones goes to my school; she is on the track team.”) While a noun can refer to an abstraction (hope, fear, wonder, etc.) the most common use, especially of a proper noun, is the “signifier” of a signified person or place, the word (here a compound) that conveys the person being referred to.   The question calls for a clear distinction from verbs, articles, adverbs, etc., and, while nouns can modify other nouns (the tollbooth ticket taker), the name is not, out of context, an adjective, like “big” or  “yellow” or “crooked.”  One of the confusions for students of English as a second language is that many words can serve both purposes—nouns and adjectives—thus obfuscating the syntax of a sentence.  Examples are “the Big Easy” and “Come indoors into the cool.”