> Þorgils kvað hana muna mundu.
> Thorgils said she would remember.
> Thorgils said of her (she?) would remember.
> Þorgils declared she would remember.

Here I think that <mundu> is 'must': ‘Þorgils said that she
must remember’. (<Mundu> is the past infinitive, here in
the usual acc. + inf. construction after <kvað>, in case
anyone was wondering about the form.)

> Eða viltu nokkuð mæla í móti þessu?"

> Do you want to say something against this?"

> Or do you want to say anything against this?”

> But do you want in-some-degree to speak against (gainsay,
> contradict) this?’

I agree with Rob and Grace that <nokkuð> here is pronominal,
not adverbial; I’d go with ‘anything’.

Brian