Jesus I know - His power to cast out devils I know. Compare Matthew 8:29.
Paul I know - Paul’s power to cast out devils, Acts . Acts 19:12.
But who are ye? - What power have you over evil spirits? By what right do you attempt to expel them? The meaning is, “You belong neither to Jesus nor Paul, and you have no right or authority to at tempt to work miracles in the name of either.”