What I’m about to write has, probably, been said already somewhere here or elsewhere.
The Original question posed about Jesus having, possibly, read the “Republic” or anything else of Plato’s works, or Greek philosophy in general, is relative to one’s take on who Jesus was. If Jesus was (is) the son of God, the question might be a moot point; God, or his Son, would be all knowing, and therefore, follows the logical conclusion. However, not so fast there, we are told by a passage in the NT. God only is all knowing, as pointed out by Jesus Himself; “Of the day and hour, only the Father knows”, and not the angels, nor even the Son." But there, Jesus was responding to the question from someone asking Him about the time that the destruction of the Temple that Jesus was prophesying, and it is referring also to when the terrible and great Day of the Lord world come (The second coming of Christ, and the Apocalypse in John’s Revelation, and also other Old Testament references by other prophets, such as Daniel, etc.) I would think, if one is a believer (Christian) that Jesus, although not knowing as much as his Father, God, would be expected to know such things as Greek philosophy, especially Plato’s Socrates, who parallels Jesus, the man, as written down in the NT, and no doubt would also know the Greek Stoics way of life, which would also parallel some of Jesus’ lifestyle and ideas. Therefore a Divine Jesus would know.
Let us assume that Jesus was just a man, and a sort of philosopher of “Kind” and a teacher of this kind of philosophy (a Jewish religion prophecy of a Messiah, which was later dramatized into early Christianity, based on the life and works of Jesus, professed and believed to have been the Jewish prophesied Messiah, but rejected by the majority of Jews, and accepted by a small minority of Jews, which then became what we all know today. Based on this assumption, then, according to some modern scholars, Jesus had the benefit of an education that exposed him to Greek philosophy, especially Stoicism. The argument of these scholars, which have to, indirectly, affirm that Jesus was just another man; albeit, a philosopher, is based on the premise that Jesus grew up in an area of Judea not as implied in the NT, but in another small town near Galilee. And nearby there was also a large and well established city (Cesarea) that was originally, basically, a Greek colony, where there was a large population of Stoics, and Stoics/Platonic philosophy institutions. These scholars believe that Jesus must have had the benefit of Stoics schooling, and for proof as to the probability, they parallel Jesus’ meek disposition, and choice of standing up and helping the poor and their life style, which was also championed by Him; same as the Stoics beliefs of humility and helping others less fortunate, and also the other moral codes. Socratic morals were also along these lines.
As far as Plato, and some other Greek philosophers of that time, and before, having been familiar with the Old Testament Bible, we have Justin Martyr as another witness. Justin claimed, as stated in Wikipedia: Justin includes a tract on Greek mythology in 1 Apol. 54 and Dial. 69 which asserts that myths about various pagan deities are imitations of the prophecies about Christ in the Old Testament. There is also a small tract in 1 Apol. 59–60 on borrowings of the philosophers from Moses, particularly Plato. These two tracts may be from the same source, which may have been an early Christian Apology. (Justin Martyr lived from 100-165 AD)
As always with these kind of hypothetical questions, which are made opaque and difficult to find by age, we can only opinion and make our best guesses at, until such time that iron clad evidence may be found. Otherwise, the moral of the story is: Only God knows for sure. But perhaps one day, if what Socrates said about the immortality of the soul is true, we can pose the questions directly to the source, and hear it directly from “the horse’s mouth.”
Long live true philosophy (truth and the search for God)