I would like to add to the hermeneutics thought. First, John 3:11 is not a stand alone verse, no verse is. This text belongs in context of the subject at hand; the paragraph, the chapter, the chapters that come before and those that come after and in harmony with the Gospels and the entire Bible.
In summary, in John chapter 1, John the Baptist had started preaching in the desert as a witness to the "light" (Jesus). The scriptures in Mark record it this way about John the Baptist, "John the Baptist appeared in the wilderness preaching a baptism of repentance for the forgiveness of sin" (Mark 1:4). The Mosaic Law prophesied of John the Baptist coming and the One (Jesus) who would follow him. (Isaiah 40:3, Mal.3:1). John was preaching and baptizing folks for confessing their sins. It's important to noticed that John rebuked the Pharisees & Sadducees because of their disbelief which is our concerned verse. John 3:11 is an extension and continuation of these men's thinking. More important is next, we see John baptizing Jesus. Jesus set the example.
In Matthew 4, Matthew recorded John the Baptist being put into prison and Jesus traveling to Galilee, Capernaum specifically, to fulfill other prophecy about Himself. While there, Jesus starts choosing His original 12 disciples (Apostles). In 4:17 the scriptures record that "from that time on Jesus began to preach, "Repent for the kingdom of Heaven has come near".
In John chapter 2, we read of the story of Jesus turning water to wine in the presence of His mother, disciples, and others. So we know Jesus already had some of His disciples. Here, His first miracle (John 2:11) was performed which set some things in motion that God did not want reversed. This miracle exposed who Jesus is and glorified God. So, the setting in John 3:11 is that the Messiah (Jesus) had arrived on earth and began His ministry to the lost, which included the nation of Israel, who were already struggling with Jesus being the Messiah found in their Laws.
From this knowledge we could easily jump to conclude that the "we" that Jesus is speaking about in John 3:11 is John the Baptist and Jesus Himself. After all, John was preaching about Jesus and Jesus was preaching too. Possibly we could include some of his apostles, but seemingly that is a stretch since Jesus had recently chosen them and had just began His teaching them and preaching to the lost. Since we don't know how long it had been from the time He chose His disciples, up to meeting Nicodemus' coming to Him that night, this is certainly speculation. We do know Jesus' ministry was only about 3 years long and He had just begun.
In John 3:13 Jesus changes to first person singular, "I", from third person "we" in verse 11. He states that, "the only one who has ever gone into Heaven is the One who came from Heaven". This is significant because here we know He has shifted from talking about more than one to talking only about Himself.
In John 3:3 Jesus brings up the topic of being born again to Nicodemus, a Pharisee, an Isrealite, a counsel man. Nicodemus is a very educated man in the Mosaic Law (Tora). He is a very public figure. A little reading in scripture and about Roman government set-up sheds quite a light on Nicodemus position. All that Jesus said to Nicodemus is logical to him and is founded in his Mosaic scriptural knowledge. (Joel 2:28,29, Zach. 12:10, Isaiah 32:14,15, Isaiah 44:3, Isaiah 4:4). The confusion in Nicodemus' thinking must be understood from his perspective, his era.
Until Jesus' death on the cross, the "mystery" of God's new kingdom was just that, a mystery to those living before the cross. Prior to Jesus' death, God had chosen a specific people to be His people. No one knew what the new kingdom would look like nor when God would establish it. They only knew it was going to happen... someday. Why would God, the creator of everything, use an impoverished family and human to establish a kingdom? And why on earth would He invite some poor dude living in the desert to introduce His King of His Kingdom? So, they had extremely little concept of a God who would allow just anyone into His kingdom.
The church that we are accustomed to, the one that Jesus established through the apostles was not imaginable. It's why the apostle Paul spoke of the "mystery of Christ" so much in his letter to the church in Ephesus (Eph.3). The gentile people were now invited to be a participant as an elite, an heir, an equal to Israel. The Israelites struggled with understanding that there was no longer to be only one nation in the Kingdom, but a kingdom made up of all nations. God now adds anyone to His church, who is washed in baptism. It is why Nicodemus went to Jesus at night. Jesus was teaching things contrary to how a man is purified from sin under the Old Law, but teaching what the prophets predicted how a man would be purified in the new kingdom. Jesus taught the new kingdom was near, as well as John the Baptist. He had indeed come.
This is the subject in the entire scriptural context of 3:11. In verse 5, Jesus mentions both water and Spirit. Nicodemus knew the Law. He knew exactly what Jesus had just pointed out. Jesus mentions the Spirit again in verses 5,6, & 8. He knew that the Law taught that a man needed a witness to validate who He was. He also knew the Law said the Spirit would testify for the Son of Man. Here Jesus is teaching Nicodemus, witnessing the truth about Himself, and having the Spirit as validity of Him being God in flesh. And that prompts Nicodemus to ask his question, "How can this be?". Nicodemus himself is privileged to lay his eyes on his Lord! How would we respond if Jesus walked up and said, "Hi, I'm Jesus!"?
"If you don't believe me, ask the Spirit!" We might quiver and say, "How can this be"? "I wasn't expecting you".
So the "we" in John 3:11 is Jesus,the Spirit, the Law, God, and yes even men like John the Baptist. There are many who witness for God. In this isolated, very private, one-on-one between Jesus and Nicodemus, Jesus needed no one except Himself. But in an effort to help Nicodemus' understanding, Jesus called on the Spirit, and the Law as witness. Why? Because Jesus came to seek and save the lost... all of us, even those in denial.
John WROTE in 3:19, "This is the verdict, light has come into the world, but people loved the darkness instead of light because their deeds were evil." John was referring to the Pharisees, teachers of the law, Sadducees, and even the gentiles who refused Jesus as the Christ and had Him crucified on the cross.