Noun
I [noun|ˈī ]: Someone aware of possessing a personal individuality.
Compare – Me, mine, my, we.

Ex. I am

Pronoun
I [First person singular pronoun|ˈī]: The one who’s writing or speaking: Self.

Ex. I don’t know

So when I say « I don’t know who I am »
Even the I’s in the phrase differ from each another.