no one is a pronoun referring to no person. As in the phrase "no one spoke out against what she said", which means that no one came out against what she said.
As a noun, the word nobody means someone of little importance. As in "he is a nobody", a derogatory expression to say that he is a person not important to that social group.
The expression John nobody is a kind of Brazilian slang to determine someone without social or economic relevance, without distinction. When you say "so-and-so was a nobody", most of the time it is said of a person without possessions, goods, and who has no social status.
It is correct to say that the nobody's grammar classification it is an indefinite pronoun as well as a masculine noun. It occupies both classes, with very similar meanings.
In the case of the phrase: "He is a nobody", we have the nobody as a masculine noun, a name to designate someone or something, preceded by the indefinite article "a".
In the phrase "there was nobody", the nobody here occupies the role of indefinite pronoun, indicating that there was no person.
As synonyms for nobody as a pronoun, we have the expressions neither person nor person. As a noun, no one can be replaced by disqualified, disqualified and unimportant.
no one or no one
The word nobody is always accented, carrying the accentuated accent in the last syllable. So no one's form is incorrect.
This is due to the oxytone rule, which states that all oxytones (words that have the last syllable as stressed syllable) must be accented if they end in A, E, O, EM, and EMS.