As discussed under Helaman 1:9, all the evidence from 𝓞 argues that this name was spelled Kishcumen. Here in 3 Nephi 9:10, 𝓞 is not extant, but both 𝓟 and the 1830 edition have the spelling Kishkumen. At this point in the transmission of the text, both Oliver Cowdery (the scribe in 𝓟) and the 1830 typesetter were spelling the name as Kishkumen, despite the probability that 𝓞 had the original spelling with the c, Kishcumen.
Here the presumption is that the city was named after Gaddianton’s fellow conspirator, Kishcumen, especially since the inhabitants of this city are identified as being especially wicked. Oliver Cowdery (when he copied the text into 𝓟) and the 1830 typesetter must have made the same assumption.
Summary: Emend the spelling Kishkumen for the city listed in 3 Nephi 9:10 to Kishcumen, under the assumption that the city was named after Kishcumen (whose name is spelled that way in the earliest textual sources).