Jesus answered (see 1.50; 2.18,19; 3.3).

You are a great teacher in Israel is literally “You are the teacher of Israel” (see Goodspeed); the Greek text does not read “you are a teacher of Israel” (see Revised Standard Version, Phillips) or “you, a teacher in Israel” (Moffatt, Jerusalem Bible). Commentators agree that the use of the definite article “the” before “teacher” is to emphasize the status and position of Nicodemus as a teacher in Israel (New English Bible “thus famous teacher of Israel”; New American Bible “You hold the office of teacher of Israel”). A great teacher in Israel may be in some languages “an important teacher among the people of Israel” or “a teacher to whom many people of Israel look for teaching.” The grammatical construction in Israel does not mean necessarily that Nicodemus was one who “taught Israel.” The more probable meaning is that “among the people of Israel, Nicodemus was a famous teacher.”

You don’t know this? may be rendered in some languages “you do not understand this?” but in order to make it an exclamatory question, one may translate “and how is it possible that you do not understand this?” This is literally “these things,” but the use of the singular or of the plural in the receptor language is purely a matter of style, so long as the antecedent is made clear.

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .