We all need a reason to believe. The question is, is the reason we’re looking for realistic or unrealistic?
Let me suggest a simple test: Have a number of credible people that you know experienced something that has made them believers? Ask for that experience yourself. Don’t go crazy. Don’t think of some bizarre cosmic test for God to pass in order to impress you. Begin with the experiences of people you know and trust.
As supernatural as God may be, he manifests himself within our natural reality. Start there.
Thomas didn’t ask for anything outlandish or special. He only asked to see the exact same thing that all the other disciples got to see: Jesus’ scars.
What have others experienced that you long to see for yourself? Ask for it. There’s no guarantees. God is not a genie, nor a circus monkey. And he doesn’t always repeat himself in the same ways for different people. But he very well might show up with something that will make you stop doubting and believe.