DID PAUL KNOW HE WAS SPEAKING TO JESUS?

Acts 9: 5. And he (Paul) said, Who art thou, Lord? And the Lord said, I am Jesus whom thou persecutest: it is hard for thee to kick against the pricks. The assumption of contradiction is that, if Paul didn't know it was Jesus, why did he call Him 'Lord'?

'Lord' has other meanings besides 'God'.  The Greek word used there (Kurios, Strongs #2962) also means 'master' or 'sir' and is used in this fashion frequently (see Matthew 21:30 for one example, usually translated in Bibles as 'sir').  Not a contradiction.