Why did Jesus ask Judas 'Friend, wherefore art thou come?'?
Jesus asked this not because He didn't know, but because He often responded with a question. He knew why Judas was there and what Judas was up to. The question therefore came at the moment of Judas's betraying kiss, showing that Jesus was not surprised by the arrest.
Les teaches that Matthew 26:49 records Judas coming to Jesus, saying 'Hail, Master,' and kissing Him, which was the clue. Then in verse 50 Jesus says, 'Friend, wherefore art thou come?' Les points out that Jesus often responded with a question, not because He didn't know. He knew why they were there and what Judas was up to. The context also notes a large group of troops had come at night to arrest Him, which Les calls ridiculous. So the question was asked by a knowing Jesus at the moment of betrayal.
And Jesus said unto him, Friend, wherefore art thou come? Then came they, and laid hands on Jesus, and took him.