"Who Am I" is broken down in the MeQ™ into both how we ground ourselves and also our sense of integrity. To be grounded is to lead a life that is generally balanced, sensible and realistic. Integrity is demonstrated in our moral attitudes and behaviors. Your personal foundation is rooted (pardon the pun) in groundedness and integrity.
"Why Do I" is usually a question we have when disconnected from our groundedness and integrity. We seek to understand so we explain our attitudes and actions either to ourselves, another person(s) or both. It is often our inner fears and judgments that create the disconnection in the first place, so increasing self-awareness in those two areas is the basis of understanding most "why" questions.
"How Do I" encapsulates our sense of knowledge. It is more concrete than "who" or "why". Not only does the question show us our perceived (or actual) knowledge gaps, it is also a more future-oriented question. Whether that future is in the next 10 minutes, the next 6 months or the next 25 years, we are looking for answers that can take us to where we want to go. By finding the answers to those questions, and doing so from a place of high self-awareness, we are accelerating the creation of our ideal self.