What does Parthenopolis mean in Latin?

Parthenopolis, a proper noun, means “a town in Bithynia, mentioned by Pliny”.

What is the genitive of Parthenopolis?

The genitive singular is Parthenopolis. Parthenopolis is feminine, third declension.

proper noun · femininethird declension

Parthenopolis f sg (genitive Parthenopolis)

declension
form	singular	plural
nominative	Parthenopolis	—
genitive	Parthenopolis	—
dative	Parthenopolī	—
accusative	Parthenopolim Parthenopolin	—
ablative	Parthenopolī	—
vocative	Parthenopolis Parthenopolī	—
locative	Parthenopolī	—

Parthĕnŏpŏlis, is, f., = Παρθενόπολις,

I. a city in Lower Mœsia, on the Euxine Sea, Plin. 4, 11, 18, § 44; Eutr. 6, 6.—

II. A town in Bithynia, Plin. 5, 32, 43, § 148.