Kada putujem, uvek nosim pasoš sa sobom.

Yes. Kada and kad both mean when.

• kada is a bit more neutral/full
• kad is very common in everyday speech and sounds slightly more conversational

So both are natural:

• Kada putujem, uvek nosim pasoš sa sobom.
• Kad putujem, uvek nosim pasoš sa sobom.

There is no important difference in meaning here.

Because Serbian uses the present tense for habitual or general actions, just like English does in sentences such as When I travel, I always carry my passport.

This sentence does not mean only I am traveling right now. It means something more general:

• whenever I travel
• as a rule
• habitually

So:

• putujem = I travel / I am traveling depending on context
• nosim = I carry / I am carrying depending on context

Here the meaning is habitual: Whenever I travel, I always carry my passport with me.

Putujem is the 1st person singular present tense of putovati = to travel.

So:

• ja putujem = I travel
• ti putuješ = you travel
• on/ona/ono putuje = he/she/it travels
• mi putujemo = we travel
• vi putujete = you travel
• oni/one/ona putuju = they travel

In the sentence, putujem matches the understood subject ja.

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

However, pasoš is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular is usually the same as the nominative singular.

So:

• nominative: pasoš
• accusative: pasoš

That is why the form does not change.

Compare that with a masculine animate noun, where the accusative usually looks different:

• nominative: prijatelj = friend
• accusative: prijatelja

Because Serbian does not have articles.

English says:

• a passport
• the passport

Serbian simply says:

• pasoš

The exact meaning depends on context. In this sentence, pasoš is understood naturally as my passport or a passport / the passport I need, depending on the situation.

Sa sobom means with me / with oneself in this kind of sentence.

It is built from:

• sa = with
• sobom = the instrumental form of the reflexive pronoun sebe

So literally it is something like with myself, but in natural English here it means with me.

In this sentence:

• nosim pasoš sa sobom = I carry my passport with me

This is a very common Serbian expression.

Because Serbian often uses the reflexive pronoun when the object refers back to the subject.

Here, the subject is the understood I, and sa sobom refers back to that same person.

That is why Serbian prefers:

• nosim pasoš sa sobom

rather than using a normal non-reflexive pronoun.

You will see the same reflexive idea in many expressions, for example:

• Poneo je knjigu sa sobom. = He took the book with him.
• Ona uvek ima telefon sa sobom. = She always has her phone with her.

Both s and sa mean with, but sa is often used for easier pronunciation.

Before words like sobom, Serbian normally uses sa, not just s, because s sobom is awkward to pronounce.

So:

• sa sobom = correct and natural

In general:

• s is the shorter form
• sa is used when pronunciation would otherwise be difficult, and in some fixed common expressions

Sobom is the instrumental singular form of the reflexive pronoun sebe.

After sa in the meaning with, Serbian uses the instrumental case.

So:

• sa + instrumental

That gives:

• sa sobom

This is a very useful pattern to remember.

Uvek means always.

It marks the action as habitual:

• Kada putujem, uvek nosim pasoš sa sobom.
• Kada putujem, nosim uvek pasoš sa sobom. — possible, but less natural
• Uvek nosim pasoš sa sobom kada putujem. — also possible

The original sentence sounds very natural because uvek comes before the main verb nosim.

So the most learner-friendly pattern is:

• uvek + verb

Because Kada putujem is a subordinate clause placed before the main clause.

Structure:

• Kada putujem = when I travel
• uvek nosim pasoš sa sobom = I always carry my passport with me

When this kind of time clause comes first, Serbian normally separates it with a comma:

• Kada putujem, uvek nosim pasoš sa sobom.

That is standard punctuation.

Usually, this sentence is better with kada.

• kada putujem = when I travel / whenever I travel
• dok putujem = while I am traveling

Kada expresses a general repeated situation very well.
Dok focuses more on the duration of the action.

So:

• Kada putujem, uvek nosim pasoš sa sobom. = Whenever I travel, I always carry my passport with me.
• Dok putujem, uvek nosim pasoš sa sobom. = While I’m traveling, I always carry my passport with me.

The second one is possible, but it highlights the ongoing period more than the general habit.

Because nosim is imperfective, and it fits a habitual/repeated action.

• nositi / nosim = to carry, to wear, to keep carrying
• poneti / ponesem = to take along, to bring along once, as a completed act

In this sentence, the speaker is talking about a regular habit, so nosim is the natural choice.

Compare:

• Kada putujem, uvek nosim pasoš sa sobom. = Whenever I travel, I always carry my passport with me.
• Poneo sam pasoš sa sobom. = I took my passport with me.

So the choice is really about aspect and the type of action.

Yes, several. For example:

• Kad putujem, uvek imam pasoš kod sebe.
• Kada putujem, pasoš je uvek sa mnom.

These are similar, but not exactly identical in nuance:

• nosim pasoš sa sobom = I carry my passport with me
• imam pasoš kod sebe = I have my passport on me / with me
• pasoš je sa mnom = the passport is with me

The original sentence is very natural and direct, especially for describing a personal habit.