Question: Is there any place in the Old Testament where God revealed that he has a son whom the Jews would recognize for certain? Thank you.
Response: An interesting question. Because, after all, they didn't recognize Him in the event, or, better put, chose not to recognize Him. Short of forcing their free will, there had to exist the possibility of a failure, from personal choice, to accept the reality of the Messiah when He came to them face to face.
It is true, that at the time Jesus came upon the scene to conduct His three and one half year ministry that was to culminate with His death for all mankind, Jewish thinking was focused not upon the necessity for the atonement for sin, but rather upon their own desire for the liberation of their country. As it has been so often said, they were looking not for the Cross but for the Crown. That is to say, most of Jesus' contemporaries wanted the Messiah, all right, but they wanted the conquering Messiah of the Second Advent, and were not particularly interested in the suffering Messiah of the First Advent. By this attitude they made it clear that they really didn't want God at all, but only wanted what God could do for them. For they made the false assumption that because they were the physical seed of Abraham, that this automatically qualified them for the deliverance God promises "on that day", temporal and eternal; they felt entitled to national deliverance rather than in need of personal salvation. This false reasoning pre-dates our Lord's generation:
Woe to you who long for the day of the Lord! Why do you long for the day of the Lord?
That day will be darkness [for you, and] not light.
Amos 5:18 [modified NIV]
There are myriad references to the coming Messiah in the Old Testament. Just in treating the symbolism of the Mosaic Law alone we would need several volumes to discuss all the references to Him, and most of these involve His sacrifice for us, His substitutionary death on our behalf (cf. every blood sacrifice). True enough that in the prophets there is a wealth of information about the coming Kingdom of God and its ruler, the Messiah. But even in a book such as Isaiah, where we have arguably the clearest vision of the glory of His coming as the King, we also have one of the most undeniable treatments of His humiliation for us (chapters 52-53).
It is understandable that many did not "get it" before the ministry of John and the actual coming of Christ (we are told by Peter that even the writers of the Old Testament eagerly desired to know the full meaning of these scriptures which spoke of Jesus' substitutionary death on our behalf: 1Pet.1:10-12). By after the prophesied ministry of announcement was fulfilled by John (Is.40:3-5; Mal.4:5-6), and, even more to the point, after the actual arrival on the scene of the Messiah Himself (made perspicuous by untold signs and wonders, even raising the dead; cf. Jn.21:25), those who rejected Him had only themselves to blame for "not seeing" (Jn.9:35-41). Had Jesus been any more obvious as the Son of God, the Son of Man, fulfilling every prophecy about Himself in such undeniable ways even as it was (compare Matt.8:16-17), it would no doubt have been impossible for anyone not to believe (and so would have erased the issue of free will):
Still, many in the crowd put their faith in Him. They said "When the Christ comes, will He do more miraculous signs than this man?"
John 7:30-31 NIV
Indeed, Jesus intimates that those among the rulers who gave Him over to death did have a sort of understanding of what they were doing (although, if they had seen the issue in complete truth from a pure heart, of course they never would have condemned Him: 1Cor.2:7-9):
"This is the heir; come, let us kill him."
Matthew 21:38 NASB
But for those who were open to following God in truth, the glory of Him was obvious:
A voice of one calling [in] the desert[.] ["P]repare the way for the Lord; make straight in the wilderness a highway for our God. Every valley shall be raised up, every mountain and hill made low; the rough ground shall become level, the rugged places a plain. And the glory of the Lord will be revealed, and all mankind together will see it. For the mouth of the Lord has spoken."
Isaiah 40:3-5 [modified NIV]
The Word became flesh and made His dwelling among us. We have seen His glory, the
glory of the One and Only, who came from the Father, full of grace and truth.
John 1:14 NIV
There is much written about this at Ichthys. Please consult these links for more information:
Who is the Messiah?
Jesus is the Messiah
Biblical Prophecies about the Messiah
The Formal Inauguration of Jesus' Ministry (in BB 4A: Christology)
The Two Witnesses of Revelation and the Ministry of the 144,000
Hope this gets to the issue of your question.
Yours in Him,