Well, Master, thou hast said the truth; for there is one God
All the best texts omit God.
Well (καλῶς)
Exclamatory, as one says good! on hearing something which he approves.
The truth ( ἐπ' ἀληθείας)
Incorrect. The phrase is adverbial; of a truth, in truth, truthfully, and qualifies the succeeding verb, thou hast said.
For (ὅτι)
The A. V. begins a new and explanatory sentence with this word; but it is better with Rev. to translate that, and make the whole sentence continuous: Thou hast truthfully said that he is one.