The quick response is this: Know, don't ask for proof.
What are you actually asking for in your need for proof of God? Who needs proof? Who is the questioner?
Jesus told you,
"if thou wilt be perfect, go and sell that thou hast, and give to the poor, and thou shalt have treasure in heaven: and come and follow me." (Mt 19:21)
"The kingdom of God cometh not with observation: Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you." (Lk 17:20)Recently someone asked me to prove the existence of God. Knowing that is impossible I turned it around and thought, why don't you try to prove that you exist the way you think you are. Show me proof that you actually are the body that you identify yourself with. You would have to tell me how you can be the body that is 10, 20, 40, 50 or 65, or maybe 789 or 3000 years old? How can you be something that does not consist of anything that is older than one year? Isn't that what any quantum physicist would tell you? None of the atoms in your body is older than one year. Some tissues are completely renewed in 3 days, for some it takes a little longer, but none is actually older than one year. So how come that you say, you are 40 or 76 years old? You must be delusional.
Not just that, looking at the Heisenberg Uncertainty Principle, you can not tell where any of the atoms of your body are at any given time, and neither can you tell me, where they are going. So, when you say, atoms and everything below them are the fundamental building blocks of what you call reality, how is it then that you are so sure of what you think to be? Or, that you can be hurt and get sick, lying in bed for years and die in the end? Who does make up all this nonsense? You claim reason in denying the existence of God, yet do you show any reason in establishing yourself as something that needs proof of anything.
Obviously, anyone who does not know God, and therefore does not communicate with Him directly, is very poor, and does not know himself. He does not know what he is doing here, where he is from, and what his purpose is. No one in his sane mind would need proof for the existence of Reality, the very Source by Which one lives. He simply knows, in his heart and mind, beyond concepts and analyzation. Reality is known in the immediacy of cause and effect, and is lost to you in your observation. Asking for proof of God is proof that you do not exist in any reasonable fashion. You must be denying the very Life you seek, or better be the denial of Life.
So, Jesus tells you, that you have to sell your investments (everything you have given value outside of yourself), and give to the poor, in order to be perfect. Giving is the proof that you have. If one is waiting objectively for God to show Himself, and prove His existence to you, you will be waiting a long time. God does not separate Himself from you, since He is your Source from Which you cannot depart. He does not know of your condition of separation. Give away your cherished ideas about yourself, and you will find you cannot be separated.
It totally requires your action, your determination to see differently and know something beyond what you pretend to be and live in. Asking for proof definitely denies that you are responsible for the way you see and experience yourself and reality. And what exactly would you do, separate from God, if you suddenly would find a proof that would satisfy your need for proof? How would that benefit you? By asking for proof you merely state your refusal to look within and find. By asking for proof you merely state you do not want to find. Seek, but do not find.
Jesus tells you, the Kingdom of God does not come with observation. Any proof would be your observation. Yet God cannot be observed. Reality is much more immediate and direct. In other words, it is subjective. In quantum physics, you learned that you cannot subtract yourself from the experiment and result that you are seeking in your need for proof. You inevitably influence the result, no matter how you set up your experiment.
God cannot be proven. You can experience Him, though. You will experience Him, when you remember who you are as His perfect creation and Son. To bring about the transformation of your mind that allows you to return home and remember God, is what A Course In Miracles is all about. You have no purpose here other than that. Separation is insanity and does not exist in Reality. Reality is your mind in its unity with the Mind of God, it is subjective, because there is only one mind, one Source of Reality. Yet, only if you think with the Mind of God, not separate from Him, can you be that. Therefore you need a transformation of mind, if you find yourself as split mind, thinking conceptual and being temporary and spatial.
If you want to KNOW God, get A Course In Miracles, and practice the daily lessons in its workbook. The proof is in the pudding. It takes YOUR action.
"How strange that the final anomaly in all so-called scientific thought is always the thinker." (Master Teacher)