“Where” is a very crucial question. The Protestant account is a circular “argument” that boils down to being able to tell the scripture is the scripture because it looks like the scripture. They have to adopt this theory because all their thousands of Protestant denominations are built on the revolutionary concept of prying loose the scripture from the greater Body of Christ that recognized and preserved the scriptures (a central pillar of Holy Tradition). The traditional Christian account of scripture is pretty straightforward and rooted in Christ: 1: Christ is the Word Incarnate. He proved His identity by His birth, death, and resurrection. 2: Christ commissioned the apostles with authority from Him to found a church and preach His gospel 3: Those apostles wrote the New Testament by the inspiration of the Holy Spirit 4: The apostles ordained direct successors, still acting by the guidance and protection of the Holy Spirit, who employed their inherited authority to unambiguously identify what the scriptures were (and importantly also taught what they meant). 5: The Christian today can read and submit to the scriptures because they were preserved and delivered to him by the witness of the Church that wields the authority given by Christ. The thing which He promised the gates of Hell would not prevail against. By submitting to the scripture, a believer submits to a direct line of Faith going back to Christ. A Faith once delivered for all to the Saints.

The scriptures are a part of Holy Tradition and you have no meaningful access to their divine authority or wisdom if you try to sever the scriptures from the Church that Christ founded. Sola Scriptura is a heresy that ultimately brings one to worship of self.

“The canon is self-authenticating, bro. No this isn’t begging the question, just grant me the King James Bible as a starting point. Yes the early-modern era reformers were the first have this idea and skipped over the actual work of the actual apostles that Christ gave ecclesial authority to. You can just tell it’s the scripture because of the way that it is. No, this isn’t circular. If you agree with my conclusion, you’re elect, and if you disagree you are clearly reprobate. All the libs who happen to have my same theory of scripture and come to skittles-feminism conclusions are just judging the self-evident facts incorrectly.” I also invite you to do some homework: https://www.goodreads.com/book/show/1664374.Sola_Scriptura

How do you get the New Testament when it did not exist when Paul wrote that? Is the word of God only the Torah which is what he referred to when he wrote that? How (and by what authority) do you define the list of books that make up the Scriptures? Some books that existed were rejected (by the Church) for various reasons.