משקפי הקריאה נמצאים בנרתיק המשקפיים.

Because משקפי is the construct form of משקפיים.

• משקפיים = glasses
• משקפי הקריאה = reading glasses

In Hebrew, when two nouns are linked in an X of Y relationship, the first noun often changes form. This is called the construct state (סמיכות).

So:

• משקפיים = glasses
• משקפי שמש = sunglasses
• משקפי הקריאה = reading glasses

Literally, משקפי הקריאה is something like the glasses of reading.

This is also because of the construct state.

In a construct chain, the definiteness of the whole phrase is usually shown on the second noun, not the first.

So:

• משקפי קריאה = reading glasses / some reading glasses
• משקפי הקריאה = the reading glasses

Even though משקפי itself does not have ה, the whole phrase is definite because הקריאה is definite.

This is a very common pattern in Hebrew.

Because משקפי הקריאה is grammatically plural.

Hebrew treats glasses as a plural noun, just like English does. So the verb has to agree with it:

• משקפי הקריאה נמצאים... = the reading glasses are located / are found...

If the subject were singular, the verb would be singular too.

Because משקפיים is grammatically treated as masculine plural.

So in the present tense:

• masculine singular: נמצא
• feminine singular: נמצאת
• masculine plural: נמצאים
• feminine plural: נמצאות

Since משקפי הקריאה is masculine plural, Hebrew uses נמצאים.

This may feel a little arbitrary at first, but noun gender in Hebrew often just has to be learned together with the word.

Hebrew often leaves out is/are in the present tense, but with location, נמצא / נמצאת / נמצאים / נמצאות is very commonly used to mean is/are located or is/are in.

So:

• משקפי הקריאה בנרתיק המשקפיים can be understood in some contexts, but it sounds more compressed and less explicit.
• משקפי הקריאה נמצאים בנרתיק המשקפיים clearly means The reading glasses are in the glasses case.

So נמצאים adds the sense of are located.

בנרתיק is made of:

• ב־ = in
• נרתיק = case / pouch / holder

So:

• בנרתיק = in a case / in the case

In this sentence it is followed by המשקפיים, so the full phrase is:

• בנרתיק המשקפיים = in the glasses case

Both are possible in Hebrew, but נרתיק המשקפיים is the more compact and natural construct-state version.

Compare:

• נרתיק המשקפיים = the glasses case
• נרתיק של המשקפיים = a case of the glasses / the case belonging to the glasses

The של version is more analytic and sometimes less natural for fixed noun combinations. For something like glasses case, Hebrew usually prefers the construct form:

• נרתיק משקפיים = a glasses case
• נרתיק המשקפיים = the glasses case

Again, this is because of the construct state.

In a construct chain, the first noun usually does not take ה, even if the whole phrase is definite. The definiteness is marked on the second noun.

So:

• נרתיק משקפיים = a glasses case
• נרתיק המשקפיים = the glasses case

Even though נרתיק has no ה, the whole phrase is definite because המשקפיים is definite.

This is exactly parallel to:

• משקפי קריאה = reading glasses
• משקפי הקריאה = the reading glasses

Yes.

The ending ־יים is part of the noun itself and does not make it definite. To say the glasses, Hebrew still adds ה־:

• משקפיים = glasses
• המשקפיים = the glasses

So in the sentence:

• נרתיק המשקפיים = the glasses case

The sentence is:

• משקפי הקריאה = subject
• נמצאים = are located
• בנרתיק המשקפיים = in the glasses case

So the order is basically:

Subject + verb + location

This is very natural Hebrew.

You could also change the order for emphasis, for example:

• בנרתיק המשקפיים נמצאים משקפי הקריאה.

This would sound more like In the glasses case are the reading glasses or The reading glasses are in the glasses case with extra emphasis on the location.

But the original sentence is straightforward and neutral.

A careful pronunciation would be:

mish-ke-FEI ha-kri-A nim-tsa-IM be-nar-TIK ha-mish-ka-PA-yim

A slightly more natural breakdown:

• משקפי — mishkefei
• הקריאה — hakri'a
• נמצאים — nimtza'im
• בנרתיק — benartik
• המשקפיים — hamishkapayim

A few notes:

• קריאה has a little break before the last syllable: kri-'a
• נמצאים also has a break: nim-tza-'im
• משקפי is stressed at the end: mishkeFEI

Yes. נרתיק is a general word for a case, pouch, holder, or sometimes sheath, depending on context.

By itself, it does not specifically mean a glasses case. That meaning comes from the full phrase:

• נרתיק המשקפיים = the glasses case
• literally: the case of the glasses

So the context tells you what kind of case it is.