What is this one answer and how do we know about the existence?
I do not like your type of skepticism because I could easily say You are not me so how do you know what I know?
I will use your matrix analogy: I could be an agent of the matrix and know the truth. Or perhaps I am outside the matrix and I know the truth and logic is upheld
I could know something, It is not what WE know but what you know. To assume that I do not know seems foolish.
For existence, there can only be 2 ways and one answer that I can comprehend, nor can everybody else. One is 'is', and 'isn't'. And there are no both. So thus, there can only be one answer. That is one axiom Humans take for granted.
Also when you talk about 'God', 'Ultimate Being' or anything alike, knowing isn't just enough. Say, even if you did know- how could you ever prove either? Then it is just as illogical to say God doesn't exist as much as vice versa. I don't know that you don't know, and I don't know whether you are human, a stupid talking dog, or a bunny with exceptional brains, or God, or an Agent within the matrix, or a person outside the Matrix. Which in that case, if you were really God or the ones that are possible to prove oneself- then you would be able to prove your existence, or prove that you really know something.
The point is, we know nothing unless somebody properly proves something. And it is not I, nor you that matters within 'we' unless you have proof for all. Then it is really just your beliefs. And that's really how far our logic goes.
What is logic anyway? Isn't it a tree of ordered thoughts within the human brain? How perfect is our brain anyway? Well, not assuming that you're Human- nor a stupid talking dog, or a bunny with an exceptional brain- but you'd have to prove that there is another sentient life form capable of communicating with 'Humans' on Earth. Anyways, logic takes part in a lot of things we do, including daily Homeworks, talking to your friends, with more or less 'logic'- but still is logic because it is our ordered thoughts however fucked up that 'order' is anyways.
So, we are Human, as an axiom on Earth- unless you want to, or can prove otherwise. There is no other life on Earth that is sentient 'enough', then Humans. Because of that, we assume you are Human. Because you are speaking a Human language. But as though Humans are so full of themselves in this tiny world, puny, small, and on the edge of galaxy would be probably unwise to say that logic can confirm everything, nor reason, nor science. Of course, it is the best possible choice we have, but you can't say it is everything. But hey, we get over our heads daily- so it shouldn't really bother us.
None.