Tôi chưa bao giờ quên hộ chiếu khi đi du lịch.

In this sentence, chưa bao giờ is the most natural way to say have never in the sense of up to now, not even once.

• chưa = not yet
• bao giờ = ever / at any time

So chưa bao giờ literally suggests not ever yet, which matches English have never very well.

By contrast, không bao giờ usually means never in a more general or absolute sense, like a rule, habit, or strong statement:

• Tôi không bao giờ hút thuốc. = I never smoke.
• Tôi chưa bao giờ quên hộ chiếu... = I have never forgotten my passport...

Both can sometimes be close in meaning, but chưa bao giờ is especially common when talking about life experience up to the present.

A natural breakdown is:

• Tôi = I
• chưa bao giờ = have never / never yet
• quên = forget
• hộ chiếu = passport
• khi = when
• đi du lịch = travel / go traveling

So the structure is roughly:

I + have never + forgotten + passport + when traveling.

Vietnamese does not need to mark tense the same way English does, so the English translation may use have never forgotten, even though the Vietnamese words themselves do not change form for tense.

Vietnamese does not conjugate verbs for tense the way English does. The verb quên stays the same whether you are talking about past, present, or future.

Time is usually understood from:

• time words
• context
• aspect markers such as đã, đang, sẽ, chưa

Here, chưa bao giờ tells you this is about life experience up to the present, so English naturally translates it as have never forgotten.

So even without a special past verb form, the meaning is clear.

Quên means to forget.

In this sentence, it means to forget to bring / to leave behind by forgetting the passport. In real usage, Vietnamese often lets context do the work, so quên hộ chiếu naturally means something like:

• forgetting your passport
• leaving your passport behind
• failing to bring your passport

It does not need an extra word like bring if the situation is obvious.

Because hộ chiếu is the direct object of quên.

Vietnamese basic word order is often:

Subject + adverb/time marker + verb + object

So here:

• Tôi = subject
• chưa bao giờ = adverbial expression
• quên = verb
• hộ chiếu = object

That gives:

Tôi chưa bao giờ quên hộ chiếu.

This is very similar to English word order in I have never forgotten my passport.

No, not in this sentence.

Vietnamese classifiers are often used with nouns when you are counting them or making them more specific, but they are not always required.

So:

• quên hộ chiếu = perfectly natural
• quên cái hộ chiếu = possible, but more specific or more conversational in some contexts

For a general statement like this, leaving out the classifier is normal.

Khi đi du lịch means when traveling or when I travel.

The subject is omitted because it is understood from the main clause. Since the sentence already begins with Tôi, Vietnamese does not need to repeat tôi again.

So:

• Tôi chưa bao giờ quên hộ chiếu khi đi du lịch.
• literally: I have never forgotten my passport when traveling.

This is very common in Vietnamese. If the subject of the second part is obvious, it is often left out.

Yes, absolutely.

Tôi chưa bao giờ quên hộ chiếu khi tôi đi du lịch is grammatical and clear. It simply repeats the subject.

The version without the second tôi sounds more natural and efficient in everyday Vietnamese because the subject is already obvious.

So:

• khi đi du lịch = more natural, more concise
• khi tôi đi du lịch = also correct, slightly more explicit

Adding khi makes the time relationship more explicit.

• khi đi du lịch = when traveling / when going on trips
• đi du lịch by itself = to travel / to go traveling

In this sentence, khi clearly links the action of forgetting with the situation of traveling.

Without khi, the sentence might still be understandable in some contexts, but khi đi du lịch is clearer and more natural here.

Literally:

• đi = go
• du lịch = travel / tourism

So đi du lịch literally means go travel or go on a trip, but in natural English it is usually just travel, go traveling, or go on vacation, depending on context.

It is a very common Vietnamese expression for leisure travel.

Examples:

• Tôi thích đi du lịch. = I like traveling.
• Mùa hè này tôi sẽ đi du lịch. = This summer I will travel / go on a trip.

It can suggest both, but the most natural interpretation is:

I have never forgotten my passport when traveling
= I have never forgotten to bring it / I have never left it behind on a trip

Vietnamese often leaves this kind of detail implicit. Context fills in the exact meaning.

If someone wanted to be more explicit, they might say something like:

• Tôi chưa bao giờ quên mang hộ chiếu khi đi du lịch. = I have never forgotten to bring my passport when traveling.

But your original sentence is already natural.

Yes, bao giờ can mean when in questions, but in other structures it often means ever / at any time.

Examples:

• Bạn đi bao giờ? = When are you going?
• Tôi chưa bao giờ... = I have never...
• Bạn đã bao giờ đến Hà Nội chưa? = Have you ever been to Hanoi?

So the meaning of bao giờ depends on the structure around it. With chưa in chưa bao giờ, it means never / not ever yet.

It can be used with any subject.

Examples:

• Tôi chưa bao giờ ăn món đó. = I have never eaten that dish.
• Anh ấy chưa bao giờ đến Nhật. = He has never been to Japan.
• Chúng tôi chưa bao giờ gặp cô ấy. = We have never met her.

So it is not tied to tôi at all. It is a general pattern for talking about things that have never happened up to now.

A learner should pay attention especially to these words:

• tôi — level-ish contour in Southern speech, different regional pronunciation exists
• chưa — keep the ưa vowel clear
• quên — long vowel sound; do not pronounce it like English queen
• hộ chiếu — two syllables with clear tones
• du lịch — both syllables should be distinct

A slow syllable-by-syllable reading is:

Tôi / chưa / bao / giờ / quên / hộ / chiếu / khi / đi / du / lịch

Vietnamese is tonal, so correct tones matter a lot. It is best to learn the sentence by listening to native audio and repeating it as a whole chunk, not only word by word.

Yes. Here are a few natural alternatives:

• Tôi chưa bao giờ quên hộ chiếu lúc đi du lịch.
• Tôi chưa từng quên hộ chiếu khi đi du lịch.
• Tôi chưa bao giờ quên mang hộ chiếu khi đi du lịch.

Differences:

• lúc instead of khi: similar, often a bit more conversational
• chưa từng: also means have never, slightly different style
• quên mang hộ chiếu: makes forgetting to bring the passport more explicit

Your original sentence is completely natural and standard.