Read the sentence. later they discovered a faint trail through the dark forest. which words are nouns?

Nouns can be counted. they are the name of a person place or thing. you can also put "the" "a" or "an" in front of them.
can you count a "discover" ?
can you count a "dark" ?
no

but
a forest
a trail

those are nouns.

On april 20, 1814, the dethroned emperor left france for the isle of  elba, where he was exiled under the terms of the treaty of fontainebleau.napoleon  would be allowed to ruleelba, which had 12,000 inhabitants. perhaps cruelly, the treaty allowed him to retain the title "emperor."