The issue here is that “believing” requires a lot of faith. It also requires you to rely on the experience and say-so of others, speculation and unverifiable beliefs. Actually knowing something requires you to have verifiable evidence of it. Believing in God is speculative. Others might tell you about God, might even have had their own experience of God, but unless you’ve had your own experience of God (whatever that means to you) all you can do is believe and hope for the best. So what then does it mean to “know God”?
Well I suppose it depends on who or what God is to you. If God is some omnipotent grey-bearded being somewhere in the sky, the chances are you aren’t going to do much better than believe in God. You aren’t going to meet that person other, perhaps than in some sort of afterlife. I want to suggest that even then it is doubtful.
If, however, God means something else to you, say, an experience of exquisite joy or a sense of connection with all that is around you, or compassion for the entire human race and all other sentient beings or what you might experience as a total engagement with Life as we know it, then you might come to know God. God will then become an experience which aligns with your definition of God.
I don’t want to define God for you, because there are endless notions of who or what God is. However, coming from my professional background, I am quite big on verifiable evidence. There is a reason that the courts don't like hearsay, or second-hand evidence: it's often unreliable. If I don’t have a clear notion or definition of something, I am not sure that I will ever actually know that something, but on top of that notion I require experiential or verifiable evidence to match the definition. Without a definition and clear evidence, all that will be left is to believe in that something, but with all the nagging doubt that can go with believing.