Learn Hardcore Greek: Κάποτε δούλευα σε άλλο γραφείο, αλλά τώρα έχω μόνιμη δουλειά σε αυτή την εταιρεία. - Once I worked in another office, but now I have a permanent job in this company.

So Κάποτε δούλευα σε άλλο γραφείο = Once / At some time in the past, I used to work at another office (it was my regular situation for a period).

δούλεψα (aorist) would mean a single, completed event:
Κάποτε δούλεψα σε άλλο γραφείο ≈ One time I worked at another office (on one occasion), which is not what is meant here about a former job situation.

What exactly does κάποτε mean here? Is it “once”, “sometimes”, or “once upon a time”?

In this sentence, κάποτε means at some time in the past / once / formerly.

Nuances:

κάποτε δούλευα… → I used to work… once / at one time in the past (no specific date, just “back then”).
It is not “sometimes” (that would more likely be μερικές φορές, καμιά φορά).
It can sometimes sound slightly story-like (“once, long ago”) but in everyday speech it’s also very normal for “back then / at one point in my life”.

So you can think: κάποτε = at some point in the past, not now.

Could I say παλιά δούλευα σε άλλο γραφείο instead of κάποτε δούλευα σε άλλο γραφείο? What is the difference?

Yes, παλιά δούλευα σε άλλο γραφείο is also correct and natural.

Difference in feel:

κάποτε: more neutral “once / at some time in the past”. Slightly more literary or detached, but still very common.
παλιά: literally “in the old days / back then”, often a bit more nostalgic or personal.

In everyday conversation, παλιά is probably even more common than κάποτε in this kind of sentence, but both are fine.

Why is it σε άλλο γραφείο and not στο άλλο γραφείο?

σε άλλο γραφείο = in another office (some different office, not specified which).
στο άλλο γραφείο = in the other office (a particular “other” office that you and the listener already know about).

Here the idea is just “I used to work in a different office (not this one)” → non-specific, so σε άλλο γραφείο is more natural.

Could I say σε ένα άλλο γραφείο instead of σε άλλο γραφείο?

Yes, σε ένα άλλο γραφείο is grammatically correct and understandable.

Small nuance:

σε άλλο γραφείο: slightly more compact and neutral: in another office.
σε ένα άλλο γραφείο: in one other office, a tiny bit more emphatic on “one” (as opposed to this one).

In practice, Greek often drops ένα when άλλο is already there, so σε άλλο γραφείο is the more typical phrasing.

Why is έχω μόνιμη δουλειά used instead of a verb like εργάζομαι or δουλεύω μόνιμα?

έχω μόνιμη δουλειά is a very common, idiomatic way to say I have a permanent job / I’m in permanent employment.

You could also say:

εργάζομαι μόνιμα σε αυτή την εταιρεία
δουλεύω μόνιμα σε αυτή την εταιρεία

They are correct, but έχω μόνιμη δουλειά focuses on the state of having a stable job, which matches the contrast with the first clause (“before I just worked somewhere else; now I have a permanent position here”). It sounds very natural when talking about job security.

What is the difference between δουλειά and εργασία?

Both can mean work / job, but their use is different:

δουλειά
- Most common in everyday speech.
- Means job, work, task, business.
- έχω δουλειά, πάω στη δουλειά are very common.
εργασία
- More formal.
- Used in official contexts (contracts, labor law, academic work).
- Also εργασία = assignment / project in school or university.

So here έχω μόνιμη δουλειά is natural, conversational Greek.
έχω μόνιμη εργασία would sound more formal or bureaucratic in comparison.

Why is it σε αυτή την εταιρεία and not σε αυτή η εταιρεία?

σε αυτή την εταιρεία uses the accusative case, because σε + noun requires the accusative.

The noun phrase:

η εταιρεία (nominative, subject: the company)
την εταιρεία (accusative, object / after prepositions: the company)

With the demonstrative:

αυτή η εταιρεία (nominative: this company – as subject)
αυτή την εταιρεία (accusative: this company – as object / after σε)

Since we have σε (in/at), we must use the accusative: σε αυτή την εταιρεία = in/at this company.

I have seen αυτήν with an -ν at the end. Should it be σε αυτή την εταιρεία or σε αυτήν την εταιρεία?

Both σε αυτή την εταιρεία and σε αυτήν την εταιρεία are accepted in modern Greek writing.

About the final -ν:

Traditionally, you keep -ν (την, αυτήν, κ.λπ.) before vowels and certain consonants.
Modern practice is more relaxed: many people write αυτή την here, others αυτήν την. Both are correct and understood.

So you don’t need to worry much: in this sentence, σε αυτή την εταιρεία is completely standard.

Why is there no word for “I” in the Greek sentence?

Greek usually omits the subject pronoun (like εγώ = I) because the verb ending already shows the person.

δούλευα → I was working / I used to work
έχω → I have

So Κάποτε δούλευα… αλλά τώρα έχω… already clearly means I used to work… but now I have….
You can say Εγώ κάποτε δούλευα… for emphasis (e.g. I used to work…), but it’s not necessary.

Can I change the word order, for example …αλλά έχω τώρα μόνιμη δουλειά…?

Yes, Greek word order is relatively flexible.

All of these are possible (with slightly different emphasis):

αλλά τώρα έχω μόνιμη δουλειά σε αυτή την εταιρεία (most neutral).
αλλά έχω τώρα μόνιμη δουλειά σε αυτή την εταιρεία (mild emphasis on the fact that now you have it).
αλλά τώρα σε αυτή την εταιρεία έχω μόνιμη δουλειά (emphasis on this company).

The original order is the most typical and neutral in everyday speech.

Should it be δουλεύω σε μια εταιρεία or δουλεύω για μια εταιρεία? Why is it σε here?

In Greek, the usual preposition with δουλεύω / εργάζομαι for a company or place is σε:

δουλεύω σε μια εταιρεία = I work at/in a company.
δουλεύω σε τράπεζα = I work at a bank.
δουλεύω στο δημόσιο = I work in the public sector.

You can sometimes see για with certain employers or clients (e.g. δουλεύω για μια ΜΚΟ = I work for an NGO), but for a normal job inside a company, σε is by far the most common. Hence: σε αυτή την εταιρεία.