Doručak je na stolu u kuhinji.

In Serbian, je is a clitic: a short, unstressed form that usually goes in second position in the sentence or clause.

So:

Doručak je na stolu u kuhinji.

sounds natural because je comes right after the first phrase element, Doručak.

This is very typical in Serbian:

• On je ovde. = He is here.
• Knjiga je na stolu. = The book is on the table.

English speakers often want to place je strictly like English is, but in Serbian its position is influenced by clitic rules.

Because after na when it means location (on), Serbian uses the locative case.

The base noun is:

• sto = table

In the locative singular:

• na stolu = on the table

So:

• sto = table
• na stolu = on the table

This case change is normal after prepositions that express location.

For the same reason: u meaning in for location takes the locative case.

The base noun is:

• kuhinja = kitchen

In the locative singular:

• u kuhinji = in the kitchen

So:

• kuhinja = kitchen
• u kuhinji = in the kitchen

Here na takes the locative because it describes where something is.

• na stolu = on the table

A very useful contrast is:

• na + locative = location
  
  • Knjiga je na stolu. = The book is on the table.
• na + accusative = movement onto something
  
  • Stavljam knjigu na sto. = I am putting the book onto the table.

So in your sentence, breakfast is already there, so Serbian uses na stolu.

Here u also takes the locative because it describes location:

• u kuhinji = in the kitchen

Again, compare:

• u + locative = location
  
  • On je u kuhinji. = He is in the kitchen.
• u + accusative = movement into
  
  • On ide u kuhinju. = He is going into the kitchen.

Since the breakfast is located in the kitchen, not moving there, u kuhinji is correct.

They describe two different kinds of location:

• na stolu = on the table
• u kuhinji = in the kitchen

So the sentence gives a more specific location: the breakfast is on the table, and that table is in the kitchen.

English works the same way conceptually:

• on the table
• in the kitchen

Serbian simply marks both phrases with case endings.

Yes, Serbian word order is fairly flexible, although some versions sound more neutral than others.

The most neutral version is:

• Doručak je na stolu u kuhinji.

You could also say:

• Doručak je u kuhinji na stolu.
• Na stolu u kuhinji je doručak.
• U kuhinji je doručak na stolu.

These all mean roughly the same thing, but the focus changes a little.

For example:

• Na stolu u kuhinji je doručak. puts more emphasis on the location.
• Doručak je na stolu u kuhinji. is a plain, neutral statement.

Just remember that the clitic je still tends to stay in second position.

Serbian normally does not use articles like English a/an/the.

So:

• doručak can mean breakfast or the breakfast, depending on context
• sto can mean a table or the table
• kuhinja can mean a kitchen or the kitchen

The listener understands definiteness from the situation, context, or word order.

That is why Doručak je na stolu u kuhinji. needs no separate word for the.

Yes. Doručak is a masculine noun.

A quick clue is that many Serbian masculine nouns end in a consonant:

• doručak
• sto
• grad

That matters when you learn adjectives and agreement later. For example:

• Topao doručak = warm breakfast

In this sentence, though, you do not see much agreement because there is no adjective modifying doručak.

Because doručak is the subject of the sentence, so it stays in the nominative case.

The structure is:

• Doručak = subject, nominative
• je = is
• na stolu u kuhinji = location phrase

Only the nouns inside the prepositional phrases change case:

• sto → stolu
• kuhinja → kuhinji

A rough English-friendly guide:

• doručak ≈ do-ROO-chak
• je ≈ ye
• stolu ≈ STO-loo
• kuhinji ≈ KOO-hin-yee

A few useful sound notes:

• č sounds like ch in chocolate
• j sounds like English y in yes
• nj is a single sound, like ny in canyon

So kuhinji is not pronounced with a hard English j sound.

Yes. Both are grammatically possible.

• na stolu u kuhinji = on the table in the kitchen
• u kuhinji na stolu = in the kitchen, on the table

The difference is mostly about focus and what feels most natural in context.

If you are simply describing where breakfast is, na stolu u kuhinji sounds very natural because it gives the more immediate location first:

1. on the table
2. in the kitchen

Yes. It is a complete sentence because je is the verb to be in the present tense.

So the structure is fully complete:

• Doručak = subject
• je = is
• na stolu u kuhinji = predicate/location

Serbian often uses biti (to be) exactly this way for location:

• On je kod kuće. = He is at home.
• Knjiga je na polici. = The book is on the shelf.

So this is a normal, complete Serbian sentence.