Podstanarka kaže da joj stan odgovara, ali da je stanarina visoka.

After kaže, Croatian uses da to introduce what someone says, thinks, knows, and so on. It works a lot like English that.

So the structure is:

Podstanarka kaže da... = The tenant says that...

There are two da clauses because there are two things she says:

• da joj stan odgovara
• ali da je stanarina visoka

This is like English She says that the apartment suits her, but that the rent is high.

Because the one verb kaže governs both clauses. Croatian does not need to repeat it.

So the sentence is understood as:

The tenant says [that the apartment suits her], but [that the rent is high].

This is very natural and efficient, just like in English.

Joj is the short dative form of ona, so it means to her or just her, depending on how you translate it.

It is used because odgovarati in this meaning works with the dative. Croatian says, literally:

The apartment suits her.

So:

• stan = the apartment
• joj = to her
• odgovara = suits / is suitable

Joj is the short, unstressed form. Njoj is the full, stressed form.

In a normal neutral sentence, Croatian usually uses the short form:

• Stan joj odgovara.

You would use njoj when you want emphasis or contrast:

• Stan odgovara njoj, ali ne njemu.
• The apartment suits her, but not him.

So in your sentence, joj is the expected natural choice.

Not in this sentence. Odgovarati can mean different things depending on context, including:

• to answer
• to suit
• to be suitable / appropriate

Here, because the subject is stan and the person is in the dative joj, the meaning is clearly suits or is suitable for.

So:

stan joj odgovara = the apartment suits her / the apartment works for her

Because the two clauses are built differently.

In the first clause, the main verb is odgovara:

• stan odgovara

In the second clause, the predicate is an adjective, visoka. Croatian needs the verb biti in the present tense here:

• stanarina je visoka

So je is the copula, meaning is.

Because visoka agrees with stanarina, which is a feminine singular noun.

Croatian adjectives must agree with the noun in gender, number, and case.

So:

• visok = masculine singular
• visoka = feminine singular
• visoko = neuter singular

Since stanarina is feminine, the correct form is visoka.

Because joj is a short unstressed pronoun, and Croatian usually places these short forms very early in the clause.

So the neutral order is:

da joj stan odgovara

This sounds natural and standard. If you move joj, the sentence may sound marked, emphatic, or less natural unless there is a special reason.

Sometimes you may hear something like that in speech, but for learners, it is better to keep the second da.

...ali da je stanarina visoka clearly shows that the second idea is also part of what she says. Without that second da, the structure is less parallel and can sound as if the speaker is stepping out of the reported statement.

So the safest and most standard version is:

Podstanarka kaže da joj stan odgovara, ali da je stanarina visoka.

Because Croatian has no articles. There is no direct equivalent of English a or the.

So:

• stan can mean an apartment or the apartment
• stanarina can mean rent or the rent

The exact meaning comes from context. If Croatian wants to be more specific, it can use words like ovaj, taj, or onaj.