Dhu Nuwas is known only from the years of his reign, fixed by Sabaic inscriptions issued under his regnal name Yusuf Asar Yathar and by Syriac Christian accounts of the Najran massacre around 523, both windows onto the final years of his rule rather than his early life. No source records a birth year.
What would resolve this A Himyarite inscription or independent South Arabian record naming Dhu Nuwas, under his own regnal name or his personal name, before the events of his reign that the surviving inscriptions and Syriac accounts already cover.
OpenSouth Arabian epigraphy, late antique Himyarite historyG. W. Bowersock, The Throne of Adulis: Red Sea Wars on the Eve of Islam