In John 18:37, Jesus claims “For this purpose I was born and for this purpose I have come into the world — to bear witness to the truth.”
—Jesus’s purpose in coming to earth is to bear witness to the truth.

In reply to that, Pilate asks Jesus in John 18:38 “What is truth?”
—Pilate, like many people, question ‘what is truth?’

Just one chapter earlier in John 17:17, Jesus prayed to the Father “Sanctify them in the truth; your word is truth.”
—The Word of God is the truth.

Earlier in John 8:31-32 to the Jews who were considering believing, Jesus said “If you abide in my word, you are truly my disciples, and you will know the truth and the truth will set you free.”
—True followers of Jesus know the truth and are set free from sin by it.

In John 14:6, Jesus boldly stated “I am the way, the truth, and the life.”
—Jesus is the truth. (In John’s Gospel, Jesus is also the Word.)

And in John’s prologue (at the very beginning of John), he wrote, “And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth.”
–Jesus is God in the flesh, and He is full of truth.