Imagine we were in a court. You bring me up on charges of not paying taxes. You claim my presence in the state makes me liable for taxes. (And you are willing to have me shot if I don't pay taxes.)
Where is your factual evidence that a state exists and that I am present in it?
Let me try my hand at this, it seems interesting.
I feel that asking to prove your existence within a state entirely relevant to the circumstances of which you are asking it. For example, in the above court scenario, there would be some sort of paper documentation signifying just cause to the government that you were avoiding taxes. There would be pay-stubs made out to you from your employer, property owned and deeds signed in your name with your handwriting, etc.
The above alone would prove that even if you were never physically in the state, you do draw and own assets in said state that are to be taxed and payed for, under the laws of that state in which your assets lie.
Now for proving your existence within a state, there is no way to prove your current existence by any other means than direct and personal contact at the moment in question. Documents, pictures, videos, all those would prove your existence at *some point* inside any given state, but could not possibly prove your current existence, much less where you exist.
However, given that there are no boundaries or parameters of the "state" in question, by simply existing you are in some sort of defined state. Currently, there is no unclaimed land anywhere in the inhabitable world, so by being alive you are existing in some state. That is proof you are in *a* state.
I will not attempt to prove the existence of a state, as the question you posed assumed the existence of any state, which by relation must also assume the existence of all legally acknowledged states.
If you are asking for proof you are in a specific state, I refer to the circumstances of the question. For example, a homeless man with no identification or physical assets or relatives may be impossible to be proven to exist under any certain identity. He exists nonetheless, which can be proven again only by immediate personal and physical contact, but he does not exist under any proven identity.
That said, a government wouldn't sue a homeless man for tax evasion. Maybe for loitering, but not tax evasion
