Trening je ne samo dobar za kondiciju nego i zabavan.

Because je is a clitic in Serbian, and clitics usually go in the second position of the sentence or clause.

So in Trening je ne samo dobar..., the first full element is Trening, and je comes right after it.

This is very normal in Serbian:

• On je umoran. = He is tired.
• Moj brat je ovde. = My brother is here.

This is the Serbian pattern for not only ... but also ...

So:

• ne samo = not only
• nego i = but also

In this sentence:

• ne samo dobar za kondiciju
• nego i zabavan

A very close alternative is ne samo ... već i ..., which means the same thing:

• Trening je ne samo dobar za kondiciju već i zabavan.

Good question. Nego can mean different things depending on context.

Here, in ne samo ... nego i ..., it is part of a fixed correlative structure meaning but also.

So here it does not mean than.

Compare:

• Veći je nego ja. = He is bigger than me.
• Ne samo pametan nego i vredan. = Not only smart but also hardworking.

Same word, different function.

Because both adjectives agree with trening.

Trening is:

• masculine
• singular
• nominative

So the adjectives must also be:

• masculine
• singular
• nominative

That is why you get:

• dobar
• zabavan

If the subject were feminine, the forms would change:

• Vežba je ne samo dobra nego i zabavna.

If it were plural:

• Treninzi su ne samo dobri nego i zabavni.

Because za often means for, and after za Serbian commonly uses the accusative case.

The noun is:

• nominative: kondicija
• accusative: kondiciju

So:

• za kondiciju = for fitness / for conditioning

In this sentence, dobar za kondiciju means good for your fitness / good for physical condition.

Not exactly.

In Serbian, kondicija usually means:

• physical fitness
• stamina
• endurance
• being in shape

So in this sentence it refers to physical condition/fitness, not just any kind of condition.

English speakers should be careful, because condition in English is much broader. Serbian often uses other words in other contexts, depending on the meaning.

Trening is a very common Serbian noun borrowed from the same source as English training.

Depending on context, it can mean:

• training
• practice
• workout
• exercise session

In this sentence, it most naturally means something like:

• training
• exercise
• working out

It is a masculine noun:

• trening
• dobar trening
• taj trening

It is grammatical, but many learners will also hear a more common everyday version:

• Trening nije samo dobar za kondiciju nego i zabavan.

That version may sound a little more straightforward to many speakers.

The sentence you were given, Trening je ne samo dobar za kondiciju nego i zabavan, is still correct; it places ne samo directly before the first adjective phrase for emphasis and balance.

So both are possible, but nije samo is often the version learners meet first.

Because Serbian often leaves out repeated forms of to be when the structure is clear.

So:

• Trening je ne samo dobar za kondiciju nego i zabavan.

works fine without repeating je.

You could also say:

• Trening je ne samo dobar za kondiciju nego je i zabavan.

That is also correct, but a bit heavier. Serbian often prefers the shorter version when the meaning is obvious.

Usually, no comma is needed in a short sentence with ne samo ... nego i ...

So this is normal:

• Trening je ne samo dobar za kondiciju nego i zabavan.

In longer or more complex sentences, some writers may use punctuation for clarity, but in a simple sentence like this, leaving the comma out is standard.

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

So trening can mean:

• training
• the training
• a workout
• the workout

The exact meaning depends on context.

That is normal in Serbian:

• Pas je u dvorištu. = The dog is in the yard / A dog is in the yard
• Trening je zabavan. = Training is fun / The workout is fun

Yes. In this sentence, nego i and već i are both possible:

• Trening je ne samo dobar za kondiciju nego i zabavan.
• Trening je ne samo dobar za kondiciju već i zabavan.

They mean essentially the same thing here. In everyday usage, both are common, though personal and regional preferences may differ.