God and Satan in the book of Job: how did they know about this conversation? Job chapter 1 vers 6 - 12 talks about God and Satan having a conversation.  Where does that story come from?  

Job does not know what is going on and I have never heard anyone talk about it. Is it a revelation or is it a tradition that helps us understand what was said in this conversation?  Who knew and who was told that this conversation was going on?  

(If there is not another Bible verse that can explain this question maybe the RCC or the Orthodox church have a tradition that can explain such a question). 

The author is not as important; how did the author know is the important part.
Great Question, I was actually wondering the same thing for a while until I did some reading.
The entire bible was written with the Inspiration of God, as found in 


  2 Timothy 3:16 NKJV
  16 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 


So basically God told the author what happened and what to write.For instance no one was there for the creation, God had to tell the author.