What is ’I.’ or ’who am I.’ is the same thing. As I will give the example of Maharishi Ramana.
The body doesn’t say.’ I.’ nobody says ’I.’ did not exist in a deep sleep.
When ’I.’ rises all rises’ find out with keen intellect, whence this.’ I’?—Maharishi Ramana.
This is the method of the, Self -inquiry. Or we can say deep meditation. According to the knowledge of Vedanta Guru teach you that you are not body and mind. It is true, but we don’t believe in it. But real Saint memorises to you again and again. By his instructions and by the study of scriptures, when you understand this theory, then he will instruct you to do mediation, which means Observation of mind. And according to your practice and Grace one day, you find that bliss in your heart. This is self-realisation or understanding who am I? this is also Nirvana or liberation.