Δεν ξέρω πού να βάλω αυτό το ντοσιέ, γιατί το γραφείο είναι γεμάτο.

Because πού here means where in an indirect question: Δεν ξέρω πού να βάλω... = I don’t know where to put...

In Modern Greek, the accent helps distinguish:

• πού = where?
• που = that / which / where as a relative word or connector

So in this sentence, the accented πού is the correct form.

Modern Greek does not normally use an English-style infinitive. Instead, it usually uses να + a verb form.

So:

• πού να βάλω = where to put
• τι να κάνω = what to do
• πώς να το πω = how to say it

You should think of να βάλω as the normal Greek way to express something like to put in this kind of sentence.

Βάλω is the aorist subjunctive form of βάζω. It refers to a single, complete action: put it somewhere once.

That fits this sentence, because the speaker is trying to decide on one placement for the folder.

Compare:

• πού να βάλω αυτό το ντοσιέ = where should I put this folder?
• πού να βάζω αυτά τα χαρτιά κάθε μέρα = where should I keep putting these papers every day?

So βάλω is used because the action is viewed as one complete act.

That is normal Greek structure. With demonstratives like this and that, Greek usually keeps the article too.

So:

• αυτό το βιβλίο = this book
• αυτή η καρέκλα = this chair
• αυτό το ντοσιέ = this folder / binder

Even though English says just this folder, Greek normally says this the folder structurally.

It is in the accusative, because it is the direct object of βάλω.

The speaker is putting what?
Αυτό το ντοσιέ.

For neuter nouns, the nominative and accusative often look the same, so you do not see a form change here:

• nominative: αυτό το ντοσιέ
• accusative: αυτό το ντοσιέ

So even though the form stays the same, its function in the sentence is accusative.

Ντοσιέ is a borrowed word, and it is neuter: το ντοσιέ.

It usually means something like:

• folder
• file
• binder

The exact English word depends on context.

A useful thing to remember is that ντοσιέ does not change much in form, so the article often tells you its gender and number.

It can mean either, depending on context.

• το γραφείο = desk
• το γραφείο = office

In this sentence, desk is the more natural meaning, because the speaker is looking for a place to put a physical item, and then says it is full.

So here το γραφείο είναι γεμάτο most likely means the desk is full.

Because γεμάτο agrees with το γραφείο, which is neuter singular.

The adjective γεμάτος changes to match the noun:

• γεμάτος = masculine
• γεμάτη = feminine
• γεμάτο = neuter

So:

• ο σάκος είναι γεμάτος
• η τσάντα είναι γεμάτη
• το γραφείο είναι γεμάτο

That is why γεμάτο is used here.

Because γιατί can mean both why and because, depending on how it is used.

• As a question: Γιατί; = Why?
• As an explanation: ..., γιατί το γραφείο είναι γεμάτο. = ...because the desk is full.

Here it introduces the reason, so it means because.

Yes. In Greek, it is very normal to put a comma before γιατί when it introduces a reason or explanation.

So:

Δεν ξέρω πού να βάλω αυτό το ντοσιέ, γιατί το γραφείο είναι γεμάτο.

This punctuation is standard and natural.

You would normally say:

Δεν ξέρω πού να το βάλω.

The object pronoun το goes before the verb form βάλω, after να.

So the pattern is:

• να το βάλω = to put it
• να τη βάλω = to put her/it
• να τους βάλω = to put them

This is a very common word order in Modern Greek.

Yes, very common. Greek often uses δεν ξέρω + question word + να + verb to express uncertainty about what action to take.

For example:

• Δεν ξέρω τι να πω. = I don’t know what to say.
• Δεν ξέρω πού να πάω. = I don’t know where to go.
• Δεν ξέρω πώς να το κάνω. = I don’t know how to do it.

So Δεν ξέρω πού να βάλω αυτό το ντοσιέ is a very natural, everyday Greek structure.