"Now they know that everything You have given me ..." (John 17:7)

"Now they know that everything You have given me comes from You." (John 17:7)

Why do 'they know' this now? 

Jesus is continuing his prayer to the Supreme Being, evidenced by this verse:
After Jesus said this, he looked toward heaven and prayed: "Father...." (John 17:1)

But Jesus has just prayed, right before this statement:

"I have revealed you to those whom you gave me out of the world. They were yours; you gave them to me and they have obeyed your word." (John 17:6) 

This means that Jesus is confirming that his followers were given to him by God. They do not belong to him. He says, "They were yours; you gave them to me ..."

This is why Jesus' followers now know that everything Jesus has - namely his followers and his teachings - come from the Supreme Being.

This makes Jesus dependent upon God. Jesus is reliant upon God.

What did God give Jesus?

Again, God not only gave Jesus his followers. God also gave Jesus his teachings:

"For I gave them the words You gave me..." (John 17:8)

The "words" are the teachings of Jesus. This is the central component of Jesus' life and purpose for coming to the earth. He did not come to "die for our sins," as purported by ecclesiastical Christian teachings. He came to teach. What did he teach? He taught what God gave him to teach.

This also explains a critical piece of who Jesus is. When one person gives words to another person to tell others, the person giving the words is the superior and the receiver of those words is subservient.

When the receiver then passes those words on to others, they become the messenger. This makes the receive the representative of the superior. This is Jesus' role. He is God's representative. And it is God that has given everything to Jesus.

Was Jesus praying to himself? 

Jesus is continuing his prayer to the Supreme Being, evidenced by it beginning with:
After Jesus said this, he looked toward heaven and prayed: "Father...." (John 17:1)
Even though these verses are clear that Jesus is praying to the Supreme Being, there are many who still teach that Jesus is God.

Not only is Jesus praying to someone who is not himself and calling that person "Father," but Jesus then says here that, "everything You have given me comes from You."

If Jesus were God, then why would "everything" need to be given to him by someone else? Isn't God self-sufficient? Does God need to be given "everything" by God?

Jesus' statement presents two individuals: A giver and a receiver. How can the receiver be the giver? How could the receiver receive anything without the separate existence of the giver?

In this case, it is obvious that Jesus is the receiver. And God - the Supreme Being - is the Giver.

This also points to the fact that the Supreme Being is not an impersonal force or void. God is a person, and this person God is giving something to Jesus. This notion that God is a person is a requisite to love. Jesus taught love for God. How could a person love an impersonal force or a void or monolith? A person can only love another person.

This is why Jesus' primary teaching was to love God: 
“‘Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 22:37-38)