Could God prove his existence and how?

The key is: the definition of God, and from here we start the test.

We want to prove that it is God by experience rather than logically then it can only be done with how sure that you are indeed met the Lord as you define?

If I define God as the biggest of everything, the source of all, then I should have experienced situations where I feel as one large and covers everything. God is omnipotent then God should be able to show this to us. It is generally known in the field of spirituality as to feel unity – feeling oneness.

Is it possible to disprove the existence of anything with certainty?

It’s not possible to disprove the existence of anything with certainty as long as there is the first law of thermodynamic.