The prophecy of Enoch
Whether Jude cites a book outside the canon as prophecy, and what that says of the canon's bounds.
Jude 1:14-15
14About these also Enoch, the seventh from Adam, prophesied, saying, “Behold, the Lord came with ten thousands of his holy ones,
15to execute judgment on all, and to convict all the ungodly of all their works of ungodliness which they have done in an ungodly way, and of all the hard things which ungodly sinners have spoken against him.”
What each tradition says
Rabbinic / Midrashic
Gottheil and Littmann note that a Book of Enoch is quoted in old Jewish and Christian literatures, including Jude 14, and was undoubtedly often used without special reference. Around 300 the Christian Church began to discredit it; after Syncellus and Cedrenus cited it in the ninth century, it was entirely lost until Bruce found two Abyssinian manuscripts in 1773.
Richard Gottheil and Enno Littmann, The Jewish Encyclopedia (1905), art. "Enoch, Books of (Ethiopic and Slavonic)" — I. Ethiopic Enoch — the book's quotation and later discredit
Patristic
Tertullian says the Jews may seem to have rejected Enoch for the very reason they rejected nearly all other portions that tell of Christ. It is no wonder they did not receive Scriptures that spoke of him whom, even speaking in their presence, they were not to receive. He adds that Enoch possesses a testimony in the Apostle Jude.
Tertullian, On the Apparel of Women (Ante-Nicene Fathers, vol. 4; trans. S. Thelwall) — Book I, ch. 3 — "Concerning the Genuineness of 'The Prophecy of Enoch'"
Catholic
Camerlynck notes that many Catholic scholars admit the prophecy of verses 14 and following is a loose, abbreviated citation from the apocryphal Book of Henoch, which existed a century before St. Jude wrote. He adds that St. Jude does not quote Henoch as a canonical book.
A. Camerlynck, The Catholic Encyclopedia (New York: Robert Appleton Company, 1910), art. "Epistle of St. Jude" — "Difficulties arising from the text" — the citation of Henoch
Orthodox
No sourced position found. Checked CCEL (ANF/NPNF: no Greek commentary on the Catholic Epistles in English; Tertullian and Origen are pre-Nicene Western/Alexandrian voices), archive.org search for a public-domain English Theophylact/Oecumenius on Jude (only modern translations; Hoskier's 1928 Oecumenius covers the Apocalypse, in Greek), pravoslavieto.com (Philaret's Catechism, Synod of Jerusalem 1899 — dogmatic texts with no treatment of Jude's Enoch citation).
Reformed / Protestant
Gill says it does not appear that Enoch wrote this prophecy or left it in writing. The fragment called Enoch is spurious and lacks this prophecy, so Jude did not take it from a book called the Apocalypse of Enoch. Rather, Jude had it from tradition credited by the Jews, or by divine inspiration.
John Gill, John Gill's Exposition of the Whole Bible — On Jude 1:14 (whether Jude took the prophecy from the book of Enoch)
Evangelical
Barnes argues there is no clear evidence Jude quoted from any book existing in his time. Although an apocryphal Book of Enoch contains a similar prediction, it is not certain it existed as early as Jude or that Jude quoted it. Both may have used a common tradition, which was handed down.
Albert Barnes, Albert Barnes' Notes on the Bible — On Jude 1:14 (the prophecy and the apocryphal book)