You can get 'inward witness' of God that you a his son like the bible says, nobody can rob you things like that. After that, just experiences with the Spirit are as convincing as anything else convincing.
You can even get proof of the other 'side', when the devil sees you you discovered things of the spirit, he just directly attacks you, he doesn't need to hide then.
You can see the evidence this world can be under something obscure just by watching what humans do.
BUt the bible says this is all crazy stuff for the ones who didn't had the new birth. So. i don't know why i tell them to unbelievers.
Even some christians don't believe God can do stuff to us, but what father just let you live all your life without giving you a little reassurance from time to time.