How can these things be?

What is happening in this passage?
Nicodemus, one of the rulers and “teacher” of Israel, is completely lost - “How can these things be?” (John 3:9) - and being chastised by Jesus, who he thinks is a street preacher.

Who does “We” in John 3:11 include?
Jesus Himself and potentially the Holy Spirit, John the Baptist and/or Jesus’ disciples.

Who else is Jesus addressing?
“You” (John 3:7, 11 & 12) is the second person plural pronoun, so Jesus is also chastising those whom Nicodemus represents.

Why does Jesus say “No one has gone up to heaven” (John 3:13)?
Jesus is alluding not to Enoch or Elijah being taken to heaven, but to Moses going up Mount Sinai in the Old Testament. All Jews, including Nicodemus, revered Moses as the one through whom they received God's Ten Commandments. Jesus is telling Nicodemus in terms that this “teacher of Israel” should have grasped that Moses only went up Mount Sinai to meet God, who came down from heaven to meet him there, but Jesus came directly “down from heaven” (John 3:13) and therefore has greater authority than “Moses” (see next verse). It should be noted that while ων (on), the Greek word translated “was” (John 3:13), is usually used in the present tense, it is being used in John 3:13 in the preter imperfect tense, which refers to something that was taking place or being done at some time in the past but not then finished (ων is used in this tense also in John 12:17 about the people that “were” with Jesus).

Is Jesus then telling Nicodemus that He is God?
See “Son of Man” (John 3:13).