Oh, thanks. Hmmm... don't know anything about classical verbs Is it a bit unusual or pretentious to use them? Or is it to create some sort of nuance? The rest of the text seems to be modern Japanese.知り: the -masu stem of 知る
も: a particle
せ: 未然形 (the imperfective form/the -nai stem) of a classical verb す, which is corresponding to する in modern Japanese
ず: 連用形 (the adverbial form/the -masu stem) of a classical negative auxiliary verb ず, which is corresponding to ない in modern Japanese
Thus, it means 知りもしないで/知りさえしないで/知ることもなく even without knowing ~.
Who says reading manga is a waste of time?Exactly.
He often says irresponsible words even without knowing the truth.
She left home even without eating breakfast.
Note that ～もせず can also mean "not to do and...". ず works as the continuous usage of the -masu stem of verbs in this case, and に can't be attached to it in this meaning.
He neither ate nor drank anything for three days.