Odvjetniku su potrebne komunikacijske vještine.

Because odvjetniku is the dative singular form of odvjetnik (lawyer).

In this sentence, Croatian uses a structure that is literally like:

To the lawyer, communication skills are necessary.

So:

• odvjetnik = lawyer
• odvjetniku = to/for the lawyer

With potreban / potrebna / potrebno / potrebni / potrebne in this kind of sentence, the person who needs something is often put in the dative.

They are in the nominative plural.

That is because komunikacijske vještine is the grammatical subject of the sentence:

• vještine = skills
• komunikacijske = communication / communicative

So the sentence is structured like:

• Komunikacijske vještine = subject
• su potrebne = are necessary / are needed
• odvjetniku = to the lawyer

Even though English would usually say A lawyer needs communication skills, Croatian here says something closer to Communication skills are necessary for a lawyer.

Because komunikacijske vještine is plural feminine, and both words agree with it:

• su = are for plural
• potrebne = feminine plural form of potreban (necessary / needed)

Agreement is with vještine, not with odvjetniku.

So:

• vještina = one skill → feminine singular
• vještine = skills → feminine plural
• therefore: potrebne su

If the subject were singular, the form would change:

• Komunikacijska vještina je potrebna. = A communication skill is necessary.

Because su is a clitic in Croatian, and clitics usually go in the second position in the sentence or clause.

Here the first element is Odvjetniku, so the clitic su comes right after it:

• Odvjetniku su potrebne komunikacijske vještine.

This is very natural Croatian word order.

You could also reorder the sentence:

• Komunikacijske vještine su potrebne odvjetniku.

That is also correct. The clitic still comes early, after the first phrase.

Very close, but not exactly the same in tone.

• Odvjetnik treba komunikacijske vještine.
  = The lawyer needs communication skills.

• Odvjetniku su potrebne komunikacijske vještine.
  = Communication skills are necessary for the lawyer.

The version with trebati is more direct and straightforward.

The version with biti potreban sounds a bit more like:

• stating a requirement
• describing what is necessary
• focusing on the thing needed rather than the person

Both are normal Croatian.

It can mean both, depending on context.

potreban / potrebna / potrebne often translates as:

• necessary
• needed
• required

In this sentence, all of these are possible in English:

• A lawyer needs communication skills.
• Communication skills are necessary for a lawyer.
• Communication skills are needed by a lawyer.

The exact best translation depends on style, not on a big grammatical difference.

It means communication skills.

The adjective komunikacijske comes from komunikacijski, meaning something like:

• related to communication
• communicational
• communication-related

So:

• vještine = skills
• komunikacijske vještine = communication skills

This is a normal Croatian expression.

Yes. Croatian word order is fairly flexible, although some orders sound more natural in certain contexts.

Possible versions include:

• Odvjetniku su potrebne komunikacijske vještine.
• Komunikacijske vještine su potrebne odvjetniku.
• Odvjetniku su komunikacijske vještine potrebne.

These all mean basically the same thing, but the emphasis shifts:

• starting with Odvjetniku highlights the lawyer
• starting with Komunikacijske vještine highlights communication skills

The original sentence is very natural.

Because Croatian normally does not have articles like English a/an/the.

So odvjetniku can mean:

• to the lawyer
• to a lawyer
• for a lawyer

Which one is intended depends on context.

In a general statement like this, English often translates it as:

• A lawyer needs communication skills or
• Communication skills are necessary for a lawyer

So Croatian leaves that distinction to context instead of using articles.

It can do either, depending on context.

Without extra context, this sentence can be understood as a general truth about the profession:

• For a lawyer, communication skills are necessary.

So even though odvjetniku is singular, it can function like English a lawyer in a general statement.

If the speaker meant a specific lawyer, the surrounding context would usually make that clear.

The biggest clue is the construction itself.

In Odvjetniku su potrebne komunikacijske vještine:

• odvjetniku is dative = the person affected
• komunikacijske vještine agrees with potrebne
• the adjective potrebne is plural feminine, matching vještine

That agreement shows that komunikacijske vještine is the grammatical subject.

So Croatian is not saying:

• The lawyer does something to communication skills

It is saying:

• Communication skills are needed by/for the lawyer

That is why vještine is nominative subject here, not an object.