Registar davalaca će pokazati interval između davanja krvi.

Registar davalaca literally means register of donors.

• registar = register, registry
• davalaca = of donors

The word davalaca is in the genitive plural because Serbian often uses the genitive after another noun to express of ....

So:

• registar = register
• registar davalaca = register of donors

The base noun is davalac = donor. Its forms include:

• singular nominative: davalac
• plural nominative: davaoci
• plural genitive: davalaca

This genitive plural form is very common after nouns like spisak, registar, lista, grupa, etc.

Yes. će pokazati is the future tense.

In Serbian, the future is often made with:

• ću, ćeš, će, ćemo, ćete, će
  • infinitive

So here:

• će = will
• pokazati = to show

Together:

• će pokazati = will show

Examples:

• On će doći. = He will come.
• Registar će pokazati... = The register will show...

In your sentence, the subject comes first:

• Registar davalaca će pokazati...

That is perfectly normal.

Yes, in many cases Serbian allows both patterns:

• će pokazati
• pokazaće

So these are both possible:

• Registar davalaca će pokazati interval...
• Registar davalaca pokazaće interval...

However, će pokazati is usually the more neutral and common pattern in modern usage, especially in standard prose and speech.

A very common alternative word order is also:

• Registar davalaca će pokazati...
• Registar će pokazati...

All of these are grammatically fine, but će pokazati is probably the form a learner will see most often.

Because pokazati is the perfective verb, while pokazivati is imperfective.

• pokazati = to show, to display, to reveal as a completed action/result
• pokazivati = to be showing, to show repeatedly/habitually

In this sentence, the idea is that the register will show or will indicate the interval as a result. That fits the perfective verb pokazati.

Compare:

• Sistem će pokazati rezultat. = The system will show the result.
  → one resulting action

• Sistem će pokazivati rezultate tokom dana. = The system will be showing results during the day.
  → ongoing or repeated

So pokazati is the natural choice here.

Yes. Interval is a normal Serbian noun, and it means interval, span, or period depending on context.

In this sentence, it means the time interval / time gap between blood donations.

So interval između davanja krvi means something like:

• the interval between blood donations
• the time gap between giving blood

This is a somewhat formal or administrative style, which fits the word registar.

The preposition između usually takes the genitive.

So after između, you expect genitive forms.

Here:

• davanje = giving, donation (as a verbal noun)
• genitive singular = davanja

That is why you get:

• između davanja krvi = between the giving of blood / between blood donations

This is a very useful pattern:

• između kuća = between the houses
• između dana i noći = between day and night
• između davanja krvi = between blood donations

Davanja here is a noun, not a finite verb.

It comes from the verb davati / dati and functions as a verbal noun:

• davanje = giving, donation

In the sentence it appears in the genitive singular:

• nominative: davanje
• genitive: davanja

So:

• između davanja krvi literally = between the giving of blood

English often prefers a more natural translation such as between blood donations, but Serbian often uses a verbal noun structure here.

Because krvi is the genitive singular of krv.

• nominative: krv = blood
• genitive: krvi = of blood

Since davanje is a verbal noun meaning giving, it can take an object-like complement in the genitive:

• davanje krvi = giving blood

So the phrase works as:

• davanja = of giving
• krvi = of blood

Together:

• između davanja krvi = between giving blood / between blood donations

Yes, it is very common and natural.

Serbian can express this idea in a few ways, for example:

• davanje krvi = giving blood
• dobrovoljno davanje krvi = voluntary blood donation
• donacija krvi = donation of blood

In everyday and institutional Serbian, davanje krvi is extremely common. It often sounds more natural than a direct noun-for-noun translation from English.

So interval između davanja krvi is a normal way to say the interval between blood donations.

For learners, the simplest explanation is this:

Serbian often uses the genitive singular verbal noun after između in this kind of abstract expression, even when English would think in plural terms.

So:

• između davanja krvi is normal and idiomatic

It refers to the act/type of event in a general sense: the interval between instances of giving blood.

You may sometimes encounter more specialized or stylistically marked forms elsewhere, but for ordinary learning purposes, između davanja krvi is the form to remember.

No, Serbian word order is fairly flexible.

Your sentence is:

• Registar davalaca će pokazati interval između davanja krvi.

Other possible orders include:

• Registar će pokazati interval između davanja krvi.
• Interval između davanja krvi će pokazati registar davalaca.
  (more marked, used for emphasis)

The most neutral version is usually the one with the subject first and the future marker before the main verb:

• Registar davalaca će pokazati...

So the sentence as given sounds normal and neutral.

Yes, it sounds fairly formal and administrative.

Words like:

• registar
• interval
• davanja krvi

make it sound like something from:

• a medical portal
• a government website
• a donor database
• an official instruction or notice

A more conversational Serbian sentence might be phrased differently, but for official or technical language, this sentence is natural.

A very helpful way is:

• Registar davalaca = the register of donors
• će pokazati = will show
• interval između davanja krvi = the interval between blood donations

So the full structure is:

• [Subject] Registar davalaca
• [Verb] će pokazati
• [Object] interval između davanja krvi

That makes it easier to see how the Serbian sentence is built.