In sententia “mox venio” “mox” quoque adverbium est, non nomen nec verbum.

Because in takes different cases depending on meaning:

• in + ablative = location: in the sentence
• in + accusative = motion into: into the sentence

Here the idea is location, so sententia is ablative singular.

Quoque means also or too.

In Latin, quoque usually follows the word it emphasizes. So mox quoque means mox, too, is an adverb. That is a little different from English, where also often comes before the word it relates to.

They are all nominative singular because they are predicate nouns with est:

• mox ... adverbium est = mox is an adverb
• non nomen
• nec verbum

They name what mox is or is not. Their forms are just their normal dictionary forms here.

Yes, in grammatical language.

In ordinary Latin:

• nomen often means name
• verbum often means word

But when talking about grammar, they can mean:

• nomen = noun
• verbum = verb

So here the sentence is using grammatical terminology.

This is a common Latin way to stack negatives:

• non = not
• nec (or neque) = and not / nor

So non nomen nec verbum means not a noun nor a verb or more naturally neither a noun nor a verb.

Because the subject is just one thing: mox.

Even though several nouns appear in the sentence, the statement is about a single word, so Latin uses singular est: mox is an adverb.

Latin word order is much freer than English word order. Putting the verb at the end is very common, especially in straightforward explanatory prose.

So mox quoque adverbium est is perfectly normal Latin. The meaning would stay basically the same if est came earlier.

Because classical Latin does not have articles like English does.

So Latin can say:

• in sententia = in the sentence
• adverbium est = is an adverb

English has to add the or an, but Latin does not.

Because it is being cited as an example expression.

When Latin mentions words directly, those words are often treated as a fixed quotation. The surrounding sentence does not make mox venio change its form. It is simply the example under discussion.

Yes. Mox is normally an adverb meaning soon or shortly.

In mox venio, it modifies the verb venio, telling you when the action happens. That is exactly what an adverb does, so the sentence is pointing out that mox is an adverb, not a noun and not a verb.