Hi "abbaelijah" The only one capable as you put it of making an unbeliever question his disbeliefs about God is the person of the Holy Spirit who convicts and convinces the world of sin. Only He has the power to reveal truth and uncover error so that we can by faith believe God.
A way to begin, would be intercessory prayer, because the Spirit searches the heart and can also bring about the changes needed as He successfully convinces the unbeliever. Every second of the day unbelievers make a decision and turn from sin and to God. How you asked, by prayer, would be my answer. The best place to start.
Do you understand what a law is? It is a principle or principles that work all the time and every time, they will govern and dominant, unless superseded by another law. For the law of the Spirit of life in Christ Jesus hath made us free from the law of sin and death. For the unbeliever there is a law still in affect called sin and death and only the Holy Spirit can break the hold it has on and over them. The effectual fervent prayers of the righteous availeth much.
Your question is indicative of one who cares about the condition of the lost. May grace and mercy open all doors for unbelievers to change their course and take heed to the Word and Spirit of God our two great heart changers.