Curtis L. answered • 06/14/19
Experienced and passionate tutor in writing and humanities!
The answer to this question depends very much on what period of Latin writing you would like to call back to. Originally in Latin writing, there was no punctuation, letter u, or even lowercase characters.
The letter u was not introduced until the Middle Ages. Before that point the letter v was used. The precursors to minuscule/lowercase letters appeared in Latin cursive during the Roman Imperial period, but they were hardly standardized. Their development was in part a symptom of people writing with pen and ink on papyri rather than carving letters into things. This distinction is even more apparent if you look to Archaic Latin inscriptions. Even now, capital letters are generally more linear than lowercase ones. These precursors to lowercase letters evolved into what are widely known as unical scripts. However, it wasn't until around the Carolingian period (780-900) that lowercase letters were developed and adopted across the greater part of Europe.
Your quote "de omnibus dubitandum" is often attributed to Rene Descartes (1596-1650). Since Descartes came well after the medieval period, features such as punctuation, lowercase letters, and the letter u would have been known and familiar. Therefore. Writing the quote as "De omnibus dubitandum" would be permissible. However, it would be written as "DE OMNIBVS DVBITANDVM" in a Classical Latin style.
I hope this clarifies things for you. If this is something you find interesting, I'd check out first chapter in Paleographia Latina, "Letters in Early Latin Miniscule (till c. 850)" by W. M. Lindsay.