No way to know. According to WIng, Nen type is decided by "nature and nurture", which seems to imply that there is a genetic component, but your upbringing is also important. Perhaps your parents' Nen type probably decides the probability that you are a certain type, and your upbringing will do the rest. I do wonder what this means for babies, though. Does their potential Nen type fluctuate until a certain age? Can they be awakened to Nen in the first place, or is that something that comes with age? If their Nen type is not yet final when they are awakened, does awakening them set it in stone?

As for Ging, since we don't know how hereditary predisposition works for Nen types, there is no way to tell. The Nen type of Gon's mother would also matter, regardless of whether she was a Nen user or not.