Njezin honorar nije velik, ali joj ta praksa puno znači.

Because njezin is a possessive adjective, and it has to agree with the noun it describes in gender, number, and case.

• honorar is masculine singular nominative
• so the correct form is njezin

Compare:

• njezin honorar = her fee
• njezina praksa = her internship/practice
• njezino iskustvo = her experience

So the ending changes depending on the noun.

Yes. njen and njezin both mean her.

In many situations:

• njen sounds more everyday and conversational
• njezin often sounds a bit more standard or careful

So njen honorar nije velik would also be understood perfectly well. Learners will often meet both forms.

Honorar usually means a fee, payment, or compensation for work, especially work that is not a regular monthly salary.

It is often used for things like:

• artistic work
• freelance work
• lectures
• one-time professional jobs

So it is not always the same as plaća or salary.
A learner should think of honorar as something like fee/pay for a particular kind of work.

Because in Croatian, the negative forms of biti = to be are written as single words:

• nisam
• nisi
• nije
• nismo
• niste
• nisu

So:

• je velik = is big
• nije velik = is not big

You do not separate ne from je here.

Here velik is a predicate adjective, used after the verb nije.

In Croatian, adjectives often appear in two forms often called:

• short/indefinite
• long/definite

After to be, Croatian very often uses the short form:

• On je visok.
• Grad je velik.
• Honorar nije velik.

So nije velik is the normal choice here.

The form veliki is more typical when the adjective stands before a noun:

• veliki honorar = a big fee / the big fee

joj means to her.

It is the dative singular form of ona = she.

So:

• joj = to her

In this sentence, it refers back to the woman already mentioned by njezin.

So the structure is roughly:

• Njezin honorar nije velik = Her fee is not big
• ali joj ta praksa puno znači = but that internship/practice means a lot to her

Because značiti often works with a dative person in Croatian.

A very common pattern is:

• nešto nekome znači
  = something means a lot / has significance to someone

Examples:

• To mi puno znači. = That means a lot to me.
• Ova prilika joj mnogo znači. = This opportunity means a lot to her.
• Njima to ništa ne znači. = That means nothing to them.

So in your sentence:

• ta praksa = the thing that has value
• joj = the person affected
• znači = means / matters

Because ta praksa is the subject of znači.

The sentence is literally structured like:

• that practice/internship = subject
• means a lot
• to her

So:

• ta praksa = nominative subject
• joj = dative indirect object / experiencer

That is why it is not something like tu praksu here.

Here praksa most likely means something like:

• internship
• practical training
• work placement
• hands-on experience

It does not necessarily mean practice in the English sense of repeating something again and again.

So depending on context, ta praksa may be better understood as that internship or that practical experience.

Yes, you could say mnogo znači too.

Both are natural:

• puno znači
• mnogo znači

In everyday speech, puno is extremely common and often feels very natural.

Here puno means a lot, so:

• puno znači = means a lot

You would not normally use vrlo here, because vrlo usually modifies adjectives and adverbs, not a verb in this way.

Because joj is a clitic, and Croatian clitics usually appear very early in the clause.

That is why joj comes right after ali here:

• ali joj ta praksa puno znači

This is a very natural Croatian word order.

You may also hear other orders for emphasis, such as:

• ali ta praksa joj puno znači

But the version in your sentence is very standard and idiomatic because clitics like joj tend to go near the beginning of the clause.

Yes, in this sentence ali means but.

It connects two contrasting ideas:

• Her fee is not big
• but that internship/practical experience means a lot to her

So the contrast is:

• the financial reward is small
• the personal/professional value is high

They both relate to she/her, but they do different jobs.

• njezin = her, as a possessive adjective

  • njezin honorar = her fee

• joj = to her, as a pronoun in the dative

  • joj znači = means a lot to her

So English uses her for both ideas, but Croatian uses different forms depending on grammatical function.