What type of pronoun is park?

'park' is not a pronoun, but a 'Common Noun'. They are preceded by the (in)definite article ( (a/an) or the).

Pronouns refer to 'he, she, it etc.,

Proper Nouns are the specific name of something or somebodt. e,g. New York, or 'Donald Trump;. The Definite Articles are NOT used. You don't say ' The New York' or 'The Donald Trump'.