Ramana Maharshi recommended that one investigates by asking the question 'Who am I?'

When asked who you are, there might be a hesitation as to what to answer; but when asked if you exist, there is no such doubt. The answer is a resounding, 'Yes, of course I exist'.
When the answer to the first question is as clear as the answer to the second question, there is understanding.
The realization is that both questions have in fact the same answer. That which is sure of its existence Â- the innermost certainty of I Am - is what you essentially are. In other words: I Am this knowing that knows that I Am.
The Hindus say Tat Tvam Asi (That, Thou Art). In the Old Testament, God says, 'I Am that I Am.' This undeniable 'I Am' is not you in the personal sense, but the universal Self.

Ramana Maharshi called the fundamental oneness of 'I Am' and the universal Self 'I-I.'

Watching from this understanding, I see how thoughts appear in 'my' awareness like clouds in a clear sky and then, without a trace, dissolve back in to it. ThereÂ's even no need to proclaim that thoughts appear in my awareness. In Awareness suffices. Thoughts and everything else simply happen.
Everything is, without a 'me' orchestrating it from behind the scenes. The ego is as non-essential to thinking or to the general functioning of the body-mind organism as Atlas is to supporting the heavens. Just as the ancient Greeks at some point realized that, in fact, there never was a titan named Atlas supporting the firmament, you can realize there never was an actual ego supporting the absolute certainty of 'I Am.'

~ From the book: Awakening to the Dream: The gift of lucid living, by Leo Hartong