It's a question to ask, not to answer.
It's a question that can create madness if you are too forceful with it.
Who Am I?That's right. I would contend that a lot of the problem with this question, which certainly plenty of memoirists are asking, is not that they are asking it. It's that they are hoping to answer it.
I am going to break the suspense: There Is No Answer.
No one answer. No memoir will capture you forever. In fact, memoir is supposed to be one aspect of you - not your whole life or whole self. Most of my students overshoot, try to cover everything, or start writing about everything in order to see if they can feel out what is underneath. This kind of feeling out is very helpful and useful, but does not replace the actual understanding that needs to come with picking out themes and structure:
It can be easy to "tell stories" about ourselves. Letting the stories tell themselves, however, is much more challenging. The most painful - and rewarding - aspect of memoir is to let yourself use it in order to keep asking this question. Not answering it. Contemplating it. These are the strongest memoirs - you can feel the surprise of the writer, either consciously stated or, if you read interviews before or after, you can hear them admit it there.
Best of all, you feel it in the writing - they are using the memoir to ask questions and explore.
Stay curious as much as you can. Stay open to finding a new you, many new yous, even in the you/s of the past. Don't try to use that writing to figure anything out - be open to it showing you ideas, questions, understanding you haven't had before. Be vulnerable. Stay alive as you write, and it will show in the writing - your life energy, not just your life.