Disclaimer: For discussion’s sake, the following post is what the Theravada Buddhist view is on non-self, I thought I would mention and discuss it since it is mentioned in the first post of the topic.
In the topic title you say: “What or who is You?” This questions implies that there is a self, a permanent essence somewhere to be found within your mind and/or body. A better question to ask is “What do I take my self to be?”, because this leaves open the possibility that there is no self, no permanent essence to be found.
Since you mentioned Buddhism and non-self, I thought I would mention what Theravada Buddhism mentions about it. In Theravada Buddhism, there are these five components of existence.
Body or Form
Feelings or Experience
Perceptions
Mental formations like thoughts and the will
Consciousnesses (Yes, 6 different types - smell, taste, touch, hearing, seeing and mind consciousness (aka knowing, the knower))
Again, according to Theravada Buddhism, Each one of these components of existence is said to be non-self, impermanent. There is nothing outside these five components of existence.
If any of these components of existence were permanent or a self you would be able to control them, and they would be permanent.
If body was self or permanent you would never get sick or age, but the body is always changing, aging and so on, getting sick. You would be able to say “may my body never get sick or age”, if it were self or permanent, but that is not possible.
If feelings were self or permanent, you could say “may I only feel happy feelings and never negative feelings”, but that is not the case in life, you cannot really control your feelings to that extent.
Perceptions are different for everyone, one day you may perceive something in one way, then years later in a different way, so it is not fixed and permanent, not-self.
Mental formations including thoughts and the will are not self or permanent, they are always changing. The will is conditioned by your past experiences and knowledge, thoughts as well, and one does not think all the time, there are gaps between thoughts or when meditating soemtimes. The will is not always there, it is changing, sometimes it is strong, sometimes weak.
Consciousnesses, the 6 different types of consciousness, are not permanent or self, including mind consciousness itself. You see something then you become aware of seeing, you hear something then you are aware of hearing, mind consciousness is arising and passing away, it is not always there, it is not constant, it does not last forever. It is difficult to see clearly because the mind is very quick, there are so many processes going on per second. Anyway another point is that you can never know for certain that something is eternal, so if mind consciousness was eternal, you would never know for sure, eternity being an infinite amount of time.