For example, dionysius' roman antiquities is somewhere around 2000 years old - presumably there were copies made and we have copies, but where can someone learn about the history of our primary sources?
Check out my contribution on Herodotus' Histories to know more about textual tradition and how ancient texts are being published today : https://www.reddit.com/r/AskHistorians/comments/fuqhqt/is_historiesherodotus_realiable_or_fiction/fmgc0wu/?utm_source=share&utm_medium=web2x
I'd add that for each and every primary source you want to study, you should look up for its latest academic edition. You will find there an introduction about the manuscripts containing the ancient text that sparked your interest, how those manuscripts relate to each other, which contain the best copies of the text, etc. Good hunting!
Did you check the book list?
Recommended reading in this case:
Scribes and Scholars: A Guide to the Transmission of Greek and Latin Literature by Reynolds and Wilson (1968). This book describes how modern readers have ancient texts to read, and how humans preserved those texts.
This should be your first port of call.