Nadležnom tijelu dostavite obrazac prijave, dokaz o vlasništvu i presliku dokumenta.

Nadležnom tijelu is in the dative singular because it marks the recipient of the action: the authority to which you submit the documents.

Breakdown:

• nadležan = competent, responsible, relevant
• tijelo = body

So literally it is something like to the competent body, but in natural English this is usually to the competent authority or to the relevant authority.

The endings show the dative:

• nadležan → nadležnom
• tijelo → tijelu

This is very common in official Croatian.

Dostavite is the imperative form of dostaviti.

More specifically, it is:

• 2nd person plural imperative

That means it can be used:

• for more than one person: Submit...
• as a polite singular: Please submit...

In official notices, instructions, and forms, Croatian often uses this form in a direct but standard administrative style.

Compare:

• dostavi = informal singular command
• dostavite = plural or polite singular command

All three are direct objects of dostavite, so they are in the accusative case. But different noun types form the accusative differently.

• obrazac is masculine inanimate
• dokaz is masculine inanimate
• preslika is feminine

In Croatian:

• masculine inanimate nouns often have the same form in nominative and accusative singular
• feminine nouns ending in -a usually change -a to -u in the accusative singular

So:

• obrazac → obrazac
• dokaz → dokaz
• preslika → presliku

That is why only presliku shows a clearly different ending here.

Because prijave depends on obrazac and means of the application / application-related.

This is a very common Croatian noun + noun structure:

• obrazac = form
• prijava = application, registration
• obrazac prijave = application form / registration form

Here:

• obrazac is the direct object, so it is in the accusative
• prijave is in the genitive singular, because it modifies the noun before it

So the structure is literally:

• form of application

English often uses noun compounds, but Croatian often uses the genitive for this relationship.

Because Croatian often uses the pattern dokaz o + locative.

So:

• dokaz = proof
• o = about / concerning
• vlasništvu = ownership, in the locative singular

Literally, dokaz o vlasništvu is proof about ownership, but in natural English we translate it as proof of ownership.

This is just a normal Croatian construction. English and Croatian often package these relationships differently.

Vlasništvu is in the locative singular.

That is because the preposition o usually requires the locative when it means about / concerning.

So:

• vlasništvo = ownership
• o vlasništvu = about ownership

This is a good pattern to remember:

• govoriti o nečemu = to talk about something
• informacija o nečemu = information about something
• dokaz o nečemu = proof of something / proof concerning something

Presliku dokumenta means a copy of the document.

Breakdown:

• presliku = accusative singular of preslika
• dokumenta = genitive singular of dokument

So the structure is:

• copy of the document

A useful note:

• preslika is a fairly formal or administrative word
• in everyday speech, many people also say kopija

In official language, preslika is very common.

Because it depends on preslika.

Croatian often expresses X of Y by putting Y in the genitive:

• preslika dokumenta = copy of the document
• obrazac prijave = application form
• broj telefona = telephone number

So dokumenta is not a separate object of the verb. It is part of the noun phrase presliku dokumenta.

Because Croatian has no articles.

English distinguishes:

• a form
• the form

Croatian usually does not mark that with a separate word. The meaning is understood from:

• context
• word order
• situation
• sometimes adjectives or pronouns

So obrazac prijave could mean:

• an application form
• the application form

The exact meaning depends on context.

Yes. Croatian word order is fairly flexible because the case endings show the grammatical roles.

This sentence begins with Nadležnom tijelu because official Croatian often puts the recipient first:

• Nadležnom tijelu dostavite...

You could also say:

• Dostavite obrazac prijave, dokaz o vlasništvu i presliku dokumenta nadležnom tijelu.

That would still be understandable, but the original sounds especially natural in administrative instructions.

Because this is a normal list in Croatian:

• obrazac prijave
• dokaz o vlasništvu
• presliku dokumenta

The conjunction i means and, and standard Croatian punctuation normally does not put a comma before the final i in a simple list.

So the punctuation here is completely standard.