Kian donacon vi volas por via naskiĝtago?

Because kian describes donacon, which is the direct object of the sentence.

In Esperanto, words that modify a noun usually match it in:

• number: singular or plural
• case: especially whether it has the -n ending

Here, donacon has -n, so kian also gets -n.

• kia donaco = what kind of gift
• kian donacon = what kind of gift (as a direct object)

So Kian donacon vi volas? literally means What kind of gift do you want?

The -n marks the direct object.

In this sentence, the thing being wanted is the gift, so donaco becomes donacon.

• Vi volas donacon. = You want a gift.
• Donaco is what is wanted, so it takes -n.

This is one of the most important features of Esperanto grammar: the direct object usually gets -n.

Kian donacon means what kind of gift or what gift.

More literally:

• kia = what kind of
• donaco = gift

So kian donacon is asking about the type or choice of gift.

In natural English, it is often simply translated as What gift do you want...?, even though Esperanto is built more like What kind of gift...

Because kio and kia do different jobs.

• kio = what, referring to a thing by itself
• kia = what kind of, describing a noun

Since donaco is already the noun, Esperanto uses kia to ask what kind of noun it is:

• Kio estas tio? = What is that?
• Kia donaco estas bona por vi? = What kind of gift is good for you?
• Kian donacon vi volas? = What kind of gift do you want?

So kia/kian is the correct choice because it modifies donaco.

Vi volas means you want.

• vi = you
• volas = want

The ending -as marks the present tense in Esperanto.

So:

• mi volas = I want
• vi volas = you want
• li/ŝi volas = he/she wants

Unlike English, the verb does not change depending on the subject:

• I want
• you want
• he wants

In Esperanto, all of those use volas.

Por means for, and via naskiĝtago means your birthday.

So:

• por = for
• via = your
• naskiĝtago = birthday

Together:

• por via naskiĝtago = for your birthday

This phrase explains the purpose or occasion of the gift.

Via means your.

It is a possessive adjective, like my, your, his, etc.

In this sentence, via describes naskiĝtago:

• via naskiĝtago = your birthday

It does not take -n here because naskiĝtago is inside a por phrase, not functioning as the direct object of the main verb.

If the noun were plural or accusative in a context that required agreement, the adjective would match:

• viaj libroj = your books
• viajn librojn = your books (as direct object)

But here:

• via naskiĝtago = singular, not accusative

Yes, naskiĝtago is one word, and it is a compound noun.

It is made from:

• naskiĝi = to be born
• tago = day

So naskiĝtago literally means birth-day, just like English birthday.

Compound words are very common in Esperanto. Usually, the final part is the main idea:

• tago = day
• naskiĝ-tago = birth-day

Yes, Esperanto word order is fairly flexible because grammar endings make the roles clear.

The normal order here is:

• Kian donacon vi volas por via naskiĝtago?

But other orders are possible, for example:

• Vi volas kian donacon por via naskiĝtago?

That said, the original version sounds the most natural for a straightforward question. Starting with kian donacon highlights the thing being asked about, similar to English What gift...

A rough pronunciation guide:

Kian donacon vi volas por via naskiĝtago?

Approximate pronunciation: KEE-an doh-NAH-tson vee VOH-las por VEE-a nahs-KEEZH-TA-go

A few useful points:

• ki sounds like kee
• c in Esperanto is always ts
• ĝ sounds like the j in judge
• stress is usually on the second-to-last syllable

So:

• KI-an
• do-NA-con
• VO-las
• na-skiĝ-TA-go

Sometimes in context, yes, but literally kian donacon is more like what kind of gift.

If you are choosing from a known set of options, English often says which gift. Esperanto may still use kian donacon in many everyday situations, but if you want to emphasize selection from specific items, learners may also encounter other ways of phrasing the question.

For basic learning, the important point is:

• kian donacon asks about the gift someone wants
• the focus is on the kind or choice of gift

Because por is a preposition, and in normal Esperanto, prepositions usually take a noun without the accusative -n.

So:

• por via naskiĝtago = for your birthday

The accusative -n is mainly used for:

1. direct objects
2. direction in some cases

Here, naskiĝtago is simply the object of the preposition por, so no -n is needed.

Word-by-word:

• Kian = what kind of
• donacon = gift (direct object form of *donaco)*
• vi = you
• volas = want
• por = for
• via = your
• naskiĝtago = birthday

So the sentence literally comes out as:

What-kind-of gift you want for your birthday?

In smooth English: What gift do you want for your birthday?