answered:
Um, well… *intense blushing*
I don’t have a set Cardassian genitalia headcanon; I use different ones across different fics and am welcome to the vast diversity of Cardassian junk the fandom has to offer.
Buuuuut, I did come up with a fairly involved headcanon for that longfic I wrote where all the protesters are telling the State to go fuck itself in the cloaca. That headcanon is a modified cloaca that plays on the fandom trope of the Cardassian penis being internal and there being—for lack of a better word—a sheath down there where Julian can put his dingle dangle during sexy times.