These verses introduce three Old Testament prophets who are not specifically mentioned in the Bible: Zenoch, Zenos, and Neum. Traditional English spellings of names in ancient languages are a little bit arbitrary because a single English letter can sometimes represent different sounds or the same sound can be represented by different letters. For instance, if an ancient name had what approximately the sound of a "k" in it, should a translator render it with a "k" or with a "c"? An additional challenge arises when we do not have any letters or sounds in English that precisely match how scholars believe a particular ancient consonant or vowel (or combination of them) was uttered.
So, with that in mind, consider the name Neum. Nephi says that Christ will be "crucified, according to the words of Neum" (1 Nephi 19:10). While we don’t have anybody in the Bible by the name of Neum, we do have an Old Testament prophet named Nahum. Perhaps these were the same individual.
As for Zenock, his name sounds a bit like Enoch, and there is an ancient book called 1 Enoch (as well as books called 2 Enoch and 3 Enoch.) 1 Enoch is preserved in the Ethiopic tradition, and it has been translated and studied at great length in recent times. There was a translation of it that was done back in 1821, but even if Joseph Smith had access to it, that translation would not have given him some of the interesting information that modern scholars, such as George Nickelsburg, have uncovered in more recent translations of the text.
Interestingly, I was struck to find in 1 Enoch a list of what are called the twenty evil "watchers." These are spirits or powers that are somewhere out there in the heavens. They participate in the cosmic and spiritual dramas that the Book of Enoch is all about, with Enoch seeing visions and being taken up into the heavens and so on. In the normal translations of 1 Enoch, what we get is just a list of the names of these so-called spirits or watchers. Samyaza is one of them, and Arakiel is another–names that will not mean anything to you unless you are told that these proper names have meanings. When translated they are things like the star of God, thunder of God, shooting star of God, the one of the mountain, the earth is power, vein of God, the cloud of God, the winter of God, the perfection of God, the sea of God, and God will guide. Now why is that significant? As you read down the list of cataclysms in 1 Nephi 19:11–16 you find the opening of the earth. We find volcanic clouds mentioned, and one of the names deals with the smoke apparently of volcanic eruption. One of them, as I have said, is called the thunder of God. Thunderings are here. You go down this list in 1 Nephi 19, and most of the physical calamities line up closely with the names of these 20 watchers (or forces) mentioned in 1 Enoch.
Nephi also refers to Zenos as having spoken about these signs: "All these things must surely come, saith the prophet Zenos." Many physical forces are going to be at play as a sign of the death of Christ: Thunderings, lightnings of his power, tempests, fire, smoke, vapor of darkness, opening of the earth, mountains which shall be carried up, the rocks of the earth must rend, groaning of the earth and so on. And does 3 Nephi report the complete fulfillment of this prophecy? It does! And almost precisely in Zenos’s order.
Nephi had spoken in some detail of the death of Jesus back in 1 Nephi 11. And Lehi did too, in 1 Nephi 10. Now Nephi is basically saying, "I am not the only one who saw this. I am not the only one who prophesied this." These verses in 1 Nephi 19 offer a fairly specific prophetic explanation of what is going to happen when Christ comes to the earth and suffers the insults and eventually the death that he will be subjected to. Here in 1 Nephi 19, Nephi calls other witness to his side, using records on the brass plates to support the truth of the coming of the Messiah, which he saw in vision.
John W. Welch, "Enoch Translated," FARMS Review 16, no. 1 (2004): 413–417.
Book of Mormon Central, "Is Anything Known of the Prophet Zenos Outside of the Book of Mormon? (Jacob 5:1)," KnoWhy 67 (March 31, 2016).