Until recently, this question was considered useless. Only those poor desolate ones needed to worry about this. The other comfortable ones were understood to get along well without asking such questions. Asking "Who am I?" would be met with "What happened to you? Is everything fine?" Given the pressures from social-media explosion and work-related stress, suddenly everyone is wondering who they are.
Asking "Who am I?" is the first step to spirituality. Am I this gross body that is available to the senses? Or, am I this mind? Or, am I the senses or breath? Am I the entirety of experience?
By the process of meditation and reflection one can gradually or quickly realize that "I" am not the body, not the senses, not the breath.
After some effort, it would be clear that the mind which provides the connection between the sense data and the knower is also not me. Most of the time, the mind is subject to three qualities: truth, passion and ignorance, being the element of nature. It works on its own and most of the time uses me for its purposes of needless worry, scheming, desiring, etc.
Emerging above the view that I am the mind is very difficult but with meditation, one can attain to such an understanding.
The harder questions is: am I this knowledge. Many people emerge out of their mind-self, i.e. the false ego and think that they are knowledge. They are not knowledge of anything particular but just knowledge. The self is an illusion.
This is a misunderstanding. The self is not an illusion. The sense of "I" is not invalid. Having been conditioned with the sense of "I" getting identified with the false ego of the mind, some people are misled to conclude that there is no "I" in the absence of false ego. There is just experience or knowledge.
What remains after the false sense of self drops off is the true sense of self. This is still the "I" but a very different and benign, constant form of "I". A lot of people waste their time waiting for the knower and the known to become one. This leads them to frustrations. In reality, once the mind is transcended, a different kind of "I"-identity does exist. We may trick ourselves to not pay attention and believe that the knower has vanished. But, the knower is still there. It is with reference to the knower that the vivid experience takes place. Experience or knowledge is also always about something. We may stop labeling things thinking we are entering non-dual state, but red will remain red, blue will remain blue, and hard will be hard, soft will be soft. That is not going to change.
Content-less knowledge is an absurdity since knowledge, by definition, is always about something. It shines upon something and illuminates an object. Knowledge is also always for somebody. I do know a lot of things, and have unique experiences. The real self does exist deep and does not have to be wished away in the dream of some non-dual paradise.
We have come to understand that our brains can provide us a wide variety of experiences and hallucinations. So, it is indeed possible to legitimately have different kinds of experiences. But, the key is to find out which one is true without getting tricked by one teaching or the other.
The basis nature of the self is knowledge, and the self is the knower. It is a very different kind of knower than the mind-self (false ego). The mind simply draws the true ego of the self and superimposes it on itself or on the body. Hence, we go around thinking, "I am this body; I am tall; I am good looking; I am rich" or "I feel depressed; I am happy". When the "I" is rescued from these false identifications, it still exists but in a very different way. It is not impulsive, artificial, judgmental or acting from memory. It is grounded in the present and is not swayed by time. It approaches everything with freshness and acts from truth.
Yes, the mind-self is a product of ignorance. The mind-self does not have free-will and is driven b y forces of nature. But the true self is different.
Some people also believe that this true self is God. They become God or the All once they discover this self. This is also false. The true self is still subject every now and then to the vagaries of nature. For such high souls, nature sends distractions. They fall for those distractions after years of sanity and then nature has a hearty laugh. Wise souls suddenly lose patience or temper. This is because they are not the All. They have tricked themselves into believing that. They cannot control their experiences. They can only choose to deal with what comes their way. Nature does not act according to their intentions. It poses various problems and puts obstacles on the way. People drawn anew to spiritual experiences get frustrated when Nature just piles on problems and nothing changes. They feel they are doing something wrong.
The truth is the true self is not independent and is not the All. But, the true self is the mode of the All, of God. The true self is one expression of God. This expression while eternal, as eternal as the primary substance of nature, cannot control its experience and cannot control nature.
Only, God, the Supreme Self of All, the repose of all the best auspiciousness, greatness, beauty, bliss and potency, expresses Himself though the modes of the individual self and nature.
The mind-self makes us believe that we are the center of the universe and that the world exists for our sake. When the world slips even narrowly from what we believe is good for us, we scream "O God! Why are you doing this to me? How did I wrong You?" This is fake religion. Fake religion provides the illusion that the world exists for our sake. Have you ever seen a cat or dog or cow challenge God and scream, "God! Why are you doing this to me?" The animal would just lick its wounds and move on. No complaining, no false sense of righteousness.
By getting trapped in false religion, we confuse ourselves that religion is bogus and God is fake. It is chiefly because of our incorrect understanding of God and relating to God through the fantasy created by the mind-self or false-ego.
However, the true religion and sense of self lead us to a different religion altogether and a different relation to God. It is very simple. We exist for God's purpose as does the rest of nature. The only difference is that nature does not have knowledge while we do. Except for the presence or absence of sentience, there is no difference between the self and nature with respect to God. They are subservient to Him and exist for His purpose alone. By patient meditation, one can see this truth.
This is liberating knowledge. Bondage comes from the false-ego which assumes that the world exists for its purposes and hankers after possessions. It tries in vain to control its environment often inflicting harm upon itself. It sees the world as being against its existence, a full blown contest that needs to be won. Instead, it suffers heavy losses and suffers from accumulating karma.
Knowing that one is subservient to God, one surrenders to God. One realizes: everything being in the hands of God, God is the only savior, our only rock. One realizes: God being the ultimate truth of all reality and the abode of auspiciousness, joy, beauty and bliss, is my only pleasure. And this is not fake. It is real. We are always connected to God; we are His expressions, His modes. All this comes from Him, resides in Him and goes into Him. He is our master residing deep within. Then, there is no confusion.
There is action, but no selfish action. The action is offered to God. There is enlightenment, knowing who one is. There is love for God from the understanding of our relationship and His greatness. There is surrender from the understanding that He is the master and controller of all.
All the yogas taught in the scriptures are not artificial devices but true states of the true self. The crux of Śrīvaiṣṇavism is to understand this deeply. Then, there is no complaining "This is not working for me. I am not able to do this constantly." It comes from understanding; it comes from the deep self. Only artificial things are hard to construct and maintain. What is true will remain when everything else falls apart.