Trills have a first name and a family name. A joined Trill replaces their family name with the symbiont's name. Thus Ezri Tigan became Ezri Dax when she was unwillingly joined.
It recently occurred to me that I don't know Jadzia's family name. There doesn't seem to be any information on Memory Alpha. I suppose it was never stated onscreen.
Are there any novels/comics/other that have given a name for her?
It isn't mentioned in the show. Moving down the canon scale to the books, we learn that her family name is Idaris.
A slender shadow, taller than any of the spires, fell across a grave marker bearing a name that was barely discernible in the waning light: JADZIA IDARIS
and
He’d known Dax for more than thirty years, through three permanent hosts: Curzon Antrani, Jadzia Idaris, and Ezri Tigan. All of them had surprised him many times during their friendships, but perhaps none more so than Ezri
