Which One Is Correct?
Both spellings are acceptable. But 'everyone' without space (as one single word) is the only correct spelling for the indefinite pronoun.
'Every one' is a noun phrase and almost always followed by 'of + noun (phrase)'.
Every one (as a two-word noun phrase) should be used when referring to each individual member of a group. It has the same meaning as 'each one'.
'Everyone' is an indefinite pronoun that indicates every member of a group of people. It has the same meaning as 'everybody', though 'everyone' is more formal.