In Vedanta, or more specifically jnana yoga and Advaita Vedanta, there is a process called neti neti which is a Sanskrit term meaning 'not this, not this.' It is an analysis of what one truly is through the process of negation. In essence, anything one can observe is not who they are in their true nature. I can observe my breathing, therefore I am not my breathing. I can observe my thoughts, therefore I am not my thoughts. I can observe my body, therefore I am not my body. And so on.
In your simplest, most basic, and truest form, who are you?
the unconditional that is all conditions