What does it mean to question God? Or how can someone question God or his doing?
What does it mean to question your mother or father? Think of it this way. If your mother or father tells you something and you disagree with them then you are questioning them. The difference with questioning God is ultimately that we cannot completely understand the mind of God, and also, in opposition to Him we would always be wrong.
If by “question God” you mean question his existence it’s simply the doubt in your mind on whether He is really there or not. Not unnatural.
ok is it a sin to question God’s doing?
No, not necessarily. For example, God sometimes allows things to happen in our lives that we do not understand, and may even cause us discomfort. If we question in our hearts and minds why he allowed it to happen, so long as we do not let our questioning lead us to loss of faith or hatred of Him, then it cannot be called sinful.