The gloss definition we have been given for HoSDo' is "energy beings".
I believe it was the notes to the Hamlet translation that explained that by the nature of energy beings, it's difficult for Klingons (or humans, for that matter) to know exactly how many energy beings there, i.e. whether there is just one present or several.
So to the best of my knowledge, we don't know exactly, but what seems most likely to me is that HoSDo' is grammatically singular but refers to an unspecified number of energy beings (possibly just one, possibly more than one).
So, a bit like "furniture" in English which is singular in English but plural Möbel in German.
I'd translate "We saw some energy beings" into HoSDo' wIlegh with the singular object suffix wI-. I'm not sure whether "We saw one energy being" would ever be something you would say (or even "We saw four energy beings", for that matter).
But I'm not sure whether HoSDo' has been used before in (Okrandian) canon, so this is partly speculation.