> Þykist eg nú sjá allt eftir
> I think-myself now to see (understand) everything accordingly (?)

As in "according to what it (each element of the dream) means"? Or
could 'eftir' be "afterwards", "in retrospect", and 'allt' refer to
all the events that have taken place? I'm not sure.

> Hvað er að orðið?

= orðit, neuter of 'orðinn', the past participle of verða.

> "Þá mun hér slægleiksmunur orðið hafa," segir Hrútur.
> ...
> "Mikill er viskumunur orðinn," segir Höskuldur,

The difference is that between Hrut (or him and Hoskuld) and who he's
up against, in this case ultimately Njal.

Grace wrote: "There were several words I couldn't find even in CV online"

Let us know if your still stuck on any words in particular, after
comparing Alan's translation. slæg- = sloeg- (Zoega spelling; CV will
have 'æ'). visku = vizku. munur = munr.

> Holtavörðuheiðar
> Wood ? heath

I think 'vörðu' here is the genitive sg. of 'varða' "cairn, heap of
stones".

> Eg þóttist sjá

"I thought myself to see", i.e. "I thought that I saw". The reflexive
ending shows that someone thinks that they themselves are doing something.