Ok I have got some ore negative feedback over the last few months, I'm wondering how do I prove I am me, and not a alt of someone?
You cant without any doubt, but if you have staked an old address you can sign a message it with if needed.
And how do I prove I am still the original owner?
Again, not without any doubt. I have posted an address with one of my earliest posts. When I sign a message with it is that proof Im still the same person? No, I could have sold the private key for that address. Is a signed message with my PGP key proof? No, I could have sold that key as well. There will always be room for doubt. As long as you stay honest and constitant in your behaviour it shouldnt really matter to most. Of course you are allowed to change, we all change over time. Im talking about drastic changes in behaviour here.
And that I haven't sold my account, signing something with a key? Is that something I would keep they key saved on my offline storage ? Are keys 2 part? And where do you get these keys from?
Offline or online does not matter for signing messages. What wallet do you? Maybe it can be used to sign messages. You can start now to associate an address with your account for the future.