## I truly know that this is so ##

Here the word "this" refers to Bildad's description.

## But how can a person be in the right with God? ##

"How can anyone win an argument with God?"

## If he wants to argue with God, he cannot answer Him once in a thousand times ##

"If anyone wants to argue with God, he would be unable to answer even one of God's questions."

## to argue ##

"to dispute"