Ja sada radim u kancelariji.

Yes. In Serbian, the verb ending often already tells you who the subject is, so ja is frequently omitted.

• radim = I work / I am working

So this sentence could also be:

• Sada radim u kancelariji.

Including ja adds a little emphasis or clarity, similar to saying I’m working in the office now rather than just Working in the office now.

Sada means now.

A very common shorter form is sad, which also means now:

• Ja sada radim u kancelariji.
• Ja sad radim u kancelariji.

Both are natural. Sad is a bit more common in everyday speech, while sada can sound slightly more full or neutral.

In Serbian, the present tense often covers both meanings:

• I work
• I am working

So radim can mean either one depending on context.

Examples:

• Radim u školi. = I work at a school.
• Ne mogu sada, radim. = I can’t now, I’m working.

In your sentence, sada strongly suggests the ongoing meaning: I am working now.

Radim comes from the infinitive raditi, meaning to work.

This is the 1st person singular present tense form:

• ja radim = I work
• ti radiš = you work
• on/ona/ono radi = he/she/it works
• mi radimo = we work
• vi radite = you work
• oni/one/ona rade = they work

So the ending -im here tells you the subject is I.

Because after u when it means in, Serbian uses the locative case.

The noun is:

• kancelarija = office

But in the locative singular it becomes:

• u kancelariji = in the office

So:

• u + locative = location

Compare:

• u kancelariji = in the office
• u školi = in the school
• u kući = in the house

Kancelariji is in the locative singular.

The base noun is:

• kancelarija (nominative singular)

After the preposition u meaning in/at, a location is normally expressed with the locative:

• u kancelariji = in the office

For many feminine nouns ending in -a, the locative singular often ends in -i:

• škola → u školi
• soba → u sobi
• kancelarija → u kancelariji

Yes, very often.

In English, we may choose in the office or at the office depending on nuance, but Serbian commonly uses u kancelariji for both general ideas.

So this can mean:

• physically in the office
• more generally at the office / at work in the office

The exact nuance usually comes from context.

Serbian word order is more flexible than English word order.

The neutral version here is:

• Ja sada radim u kancelariji.

But you could also hear:

• Sada radim u kancelariji.
• Radim sada u kancelariji.
• U kancelariji sada radim.

These versions are not always equally neutral; changing the order can shift emphasis.

For example:

• Sada radim u kancelariji. emphasizes now
• U kancelariji radim sada. emphasizes in the office

So the original sentence is a natural, straightforward word order, but not the only possible one.

No. Kancelarija is a very common and standard word for office.

Another common word is:

• ured

Which one you hear more can depend on region and variety:

• kancelarija is widely used
• ured is especially common in Croatian, but it can also be understood more broadly in the region

For Serbian specifically, kancelarija is a very normal choice.

A simple pronunciation guide is:

• Ja ≈ ya
• sada ≈ SA-da
• radim ≈ RA-dim
• u ≈ oo
• kancelariji ≈ kan-tse-la-RI-yi

Very roughly together:

• ya SA-da RA-dim oo kan-tse-la-RI-yi

A few useful pronunciation notes:

• j is pronounced like English y in yes
• c is pronounced like ts
• r is rolled or tapped
• Serbian vowels are usually clear and short, without much diphthong sound

Yes. Raditi is an imperfective verb.

Imperfective verbs are used for:

• ongoing actions
• repeated actions
• general habits

That fits this sentence well, because radim can mean:

• I am working now (ongoing action)
• I work (general situation)

Serbian does not usually use a special continuous tense like English am working. Instead, it often uses the present tense of an imperfective verb and lets context do the work.

Yes, it could, depending on context.

Because sada means now, it can refer to:

• right now, at this moment
• nowadays / at present

So the sentence might mean either:

• I am working in the office right now
• I work in an office now / these days

If you want to make right now very clear, context or intonation usually does that. Serbian often leaves this kind of distinction to the situation rather than marking it with a separate verb form.