You will seek Me, and even as I said to the Jews, Where I am going, you cannot come, now I say to you also. A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another. By this shall all men know that you are My disciples, if you have love for one another. Simon Peter said to Him, Lord, where are You going? Jesus answered him, Where I go you cannot follow Me now, but you will follow later. Peter said to Him, Lord, why can't I follow You now? I will lay down my life for You.
(I have a question: When did they seek Him?) But Peter' brain, in John 13:33-37, skips over the matter of loving one another and gloms onto our Lord Jesus' statement that He's going, asking where. The Lord's given hints and spoken directly where throughout the Gospels, but few people got it, maybe only one, 12:7. Peter's next comment, though, unconsciously answers his first, and hits the nail on the head (compare 11:51).
13--17 appears chronological, all the conversation and doing taking place the evening of the Passover and Lord's suppers, fuller than the other Gospels. (I always took John as the most chronological. Doing a harmony here would be especially enjoyable.) Our Lord was going away, briefly, for "3 days" (only about 42 hours), to death, resurrection, and His Father, before returning. 14:2-3, for example, refer to this. Christians, mostly, seem to have mistaken 14:2-3 to speak of a long or 2000 or so -year going and Parousia yet to be. But that's not what Christ speaks of.
If I go and prepare a place for you, I am coming again and will receive you to Myself, so that where I am you also may be. And where I am going you know the way. Thomas said to Him, Lord, we do not know where You are going; how can we know the way? Jesus said to him, I am the way and the reality and the life; no one comes to the Father except through Me.
Thomas in 14:3-6 had the same nonunderstanding and question as Peter. Jesus also is talking about the living Triune God (14:10, 17), who is God; beyond our wildest imaginings. Maybe that's why resurrection and the Triune God share the same number: 3. In any case, Philip takes a turn showing his ignorance (we'd all likely have done the same), 14:8. Then Judas (not Iscariot) asks a broader question--seems really good to me: "What has happened that You are to manifest Yourself to us and not to the world?" 14:22. It occurred to me that Judas Iscariot, even if not knowing his betrayal would be to death (Mt 27:4), may have been consciously closer to the realization of a negative-going than the others (Jn 13:2, 11, 18, 21, 26-30).
To ultimately try to answer Tony's question (my one-sentence answers get deleted): enough time has elapsed, between 13:36; 14:5 and 16:5. Our Lord, in Jn 15, speaks of fruit-bearing (and pruning; not of eternal damnation, that's for sure) and of love and joy. But then, in 15:18--16:4, most immediately to 16:5: about hate and persecution against them from the world. This one paragraph should've been my answer Tony. The hate/persecution colloquy is why none of them asks where He's going. They're saddened and sobered, although they still have the question and don't exactly know what He's going to experience (16:17-19). So He draws it out of them:
Jesus knew that they wanted to ask Him and He said to them, Are you inquiring among yourselves concerning this, that I said, A little while and you do not behold Me, and again a little while and you will see Me? Truly, truly, I say to you that you will weep and lament, but the world will rejoice; you will be sorrowful, but your sorrow will be turned into joy. A woman, when she gives birth, has sorrow because her hour has come; but when she brings forth the little child, she no longer remembers the affliction because of the joy that a man has been born into the world. Therefore you also now have sorrow; but I will see you again and your heart will rejoice, and no one takes your joy away from you. And in that day... (16:19-24).
The (new) man being born into the world is, in fact, the one new man Paul describes in Ephesians. Composed of Christ with His Body, begotten in the eternal life. "I will see you again," "in that day" are not His second coming at the end of the age. But His return in resurrection and regeneration "three days and nights" after His crucifixion (Jn 20:22; 1 Pet 1:3.) "Finally" He does speak very plainly. But they, in claiming so, still don't get it. So it's left up for them to experience it, for them to know Him.
...His disciples said, Behold, now You are speaking plainly and not saying any parable. Now we know that You know all things and have no need that anyone ask You; by this we believe that You came forth from God. Jesus answered them, Do you now believe? Behold, an hour is coming, and has come, that you will be scattered each to his own place and will leave Me alone; yet I am not alone, because the Father is with Me. These things I have spoken to you that in Me you may have peace. In the world you have affliction, but take courage; I have overcome the world. (16:25-33).
Now that's an intriguing phrase: "...and have no need that anyone ask You." Directly related to asking questions of Him. It sounds like they're thinking He was unsure, or that their questions had been to help Him clarify His ideas