Well, despite what some TV preachers will claim, God's not a genie that grants magic wishes if you pray right. And He's not an animal that does tricks on command. So it's hard for me to say exactly how he will respond if you (or anyone else) start asking Him about the big questions of life.

That being said, the Bible does say that if a son asks for bread, his father would not give him stones. So if someone asks God to make it clear that He exists and cares, God could literally start talking out loud if He felt that was best. But that's not typically my experience. Personally, I've heard God speak through feelings of conscience, relevant scriptures, wise words from godly people, a change in my heart over the course of a prayer, or serendipitous circumstances.

I'll be honest, it takes a certain level of trust in God for any of it to make sense. If someone approaches God with a sneer, I wouldn't count on God responding. If your child or SO spitefully challenged you to prove yourself, what would you do? That being said, God has a habit of going above and beyond for me.