John Lightfoot on John 18:38

[What is truth?] Christ had said, "For this cause came I into the world, that I should bear witness to the truth": q.d. "I will not deny but that I am a king, as thou hast said; for for this end I came, that I should bear witness to the truth, whatever hazards I should run upon that account." Upon this Pilate asks him, What is truth? that is, "What is the true state of this affair? that thou, who art so poor a wretch, shouldst call thyself a king, and at the same time that thou callest thyself a king, yet sayest thy kingdom is not of this world? Where lies the true sense and meaning of this riddle?"

But supposing when Christ said, he came "that he should bear witness to the truth," he meant in general the gospel; then Pilate asks him, What is that truth? However, the evangelist mentions nothing, either whether our Saviour gave him any answer to that question, or whether indeed Pilate stayed in expectation of any answer from him.