Learn Hardcore Croatian: Njen posao je ponekad naporan, ali je ona ljubazna prema svakom gostu. - Her job is sometimes tiring, but she is kind to every guest.

First clause: Njen posao je ponekad naporan – je belongs to posao.
Second clause: ali je ona ljubazna prema svakom gostu – je belongs to ona.

You must keep the second je here.
Without it (…ali ona ljubazna…), the second clause is ungrammatical in standard Croatian.

Why does je stand after posao and after ali? Could I say Je njen posao ponekad naporan or ali ona je ljubazna?

Je is a clitic (an unstressed short form) and must obey very strict word‑order rules:

In statements, je usually comes in the second position in the clause, after the first stressed word or phrase:
- Njen posao je ponekad naporan.
- Ali je ona ljubazna…

Some alternatives that are OK:

Njezin posao ponekad je naporan.
Ali ona je ljubazna prema svakom gostu. (slightly different emphasis, but correct)

But you normally cannot start a neutral statement with je:

✗ Je njen posao ponekad naporan – wrong as a neutral statement (it can appear in questions, though: Je li njen posao ponekad naporan?).

Why is it Njen posao, not Njena posao or Njeno posao?

The possessive adjective must agree with the noun in gender, number, and case:

posao = masculine singular nominative
So the possessive form must also be masculine singular nominative: njen / njezin

Forms:

njen posao / njezin posao – correct (masculine)
njena knjiga – correct for a feminine noun
njeno dijete – correct for a neuter noun

So Njena posao and Njeno posao are wrong because posao is not feminine or neuter.

Why is ljubazna feminine, when posao (job) is masculine?

Ljubazna describes ona (she), not posao:

Subject of the first clause: Njen posao → naporan (masculine)
Subject of the second clause: ona → ljubazna (feminine)

Adjectives agree with the subject they describe:

posao je naporan – masculine singular
ona je ljubazna – feminine singular

Why do we say prema svakom gostu and not prema svakog gosta?

Because the preposition prema requires the dative case, not accusative or genitive.

prema
- dative → prema svakom gostu
  - svakom = dative singular masculine of svaki
  - gostu = dative singular of gost

Prema svakog gosta is ungrammatical in standard Croatian.

Why is it svakom and not svaki in prema svakom gostu?

Svaki must agree in case with gostu:

Base form: svaki gost – nominative (subject form)
After prema you need dative:
- svakom gostu – dative singular masculine

So:

Nominative: svaki gost
Dative: svakom gostu

Because the preposition forces the dative, you must use svakom, not svaki.

What is the difference between prema svakom gostu and prema svim gostima or just prema gostima?

All are grammatical, but they have slightly different nuances:

prema svakom gostu – literally towards every guest, stressing each individual guest.
prema svim gostima – towards all (the) guests, stressing the whole group as a set.
prema gostima – more general: towards guests / towards the guests, no extra emphasis on each or all.

In your sentence, prema svakom gostu subtly highlights that there are no exceptions: she is kind to every single guest.

Can we leave out ona and just say …ali je ljubazna prema svakom gostu?

Yes, and that’s very natural in Croatian:

Njen posao je ponekad naporan, ali je ljubazna prema svakom gostu.

Croatian usually omits subject pronouns when the subject is clear from context and verb endings.
Keeping ona adds emphasis, often contrastive:

…ali je ONA ljubazna… – but she (at least) is kind… or but SHE is kind (even if others aren’t).

So:

Without ona → neutral.
With ona → slight emphasis or contrast.

Can ponekad move around? For example, can I say Njen posao ponekad je naporan or Ponekad je njen posao naporan?

Yes. Adverbs like ponekad are quite flexible:

All of these are possible and natural:

Njen posao je ponekad naporan.
Njen posao ponekad je naporan.
Ponekad je njen posao naporan.
Ponekad njen posao je naporan. (less common, but still possible)

The meaning remains “Her job is sometimes hard”.
Different positions can slightly shift emphasis (for example, starting with Ponekad highlights sometimes), but there is no big change in meaning.

What is the nuance of naporan here? Could you also say težak or zahtjevan?

All three can be used, but they have different shades of meaning:

naporan – tiring, demanding, exhausting (physically or mentally).
Focus on the effort / fatigue it causes.
težak – literally heavy; in this context: hard, difficult.
More general difficulty; can be emotional, intellectual, or practical.
zahtjevan – demanding, requiring a lot (skills, time, concentration).
Focus on high demands / complexity.

In your sentence:

Njen posao je ponekad naporan – you imagine she gets tired; the job wears her out at times.
Njen posao je ponekad težak – emphasizes that it’s not easy.
Njen posao je ponekad zahtjevan – suggests it requires a lot of effort, attention, or skill.

Could we use iako instead of ali? For example: Iako je njen posao ponekad naporan, ona je ljubazna prema svakom gostu. What’s the difference?

Yes, that sentence is correct, but ali and iako do different jobs:

ali = but (coordinating conjunction)
Connects two statements in contrast:
- …naporan, ali je ona ljubazna…
  → Her job is sometimes hard, but she is kind…
iako = although / even though (subordinating conjunction)
Introduces a concession clause:
- Iako je njen posao ponekad naporan, ona je ljubazna…
  → Although her job is sometimes hard, she is kind…

Both show a contrast, but ali just links two clauses, while iako makes the first clause subordinate and backgrounded (a condition that surprisingly doesn’t change the second fact).

What is the full declension of gost and what gender is it?

Gost is a masculine noun. Its singular and plural forms (standard variety) are:

Singular:

Nominative: gost (guest)
Genitive: gosta
Dative: gostu
Accusative: gosta
Vocative: goste!
Locative: gostu / gostu (same form)
Instrumental: gostom

Plural:

Nominative: gosti
Genitive: gostiju
Dative: gostima
Accusative: goste
Vocative: gosti!
Locative: gostima
Instrumental: gostima

In your sentence, gostu is dative singular after prema: prema svakom gostu.