Ne znam kuda ova staza vodi kad padne mrak.

Kuda is used when the idea is movement along a route or in a direction.

A useful contrast is:

• gdje = where? (location)
• kamo = where to? (destination)
• kuda = which way? along where? by what route?

Because staza means path/trail, Croatian naturally uses kuda: the question is not just a location, but where the path goes.

So kuda ova staza vodi is literally close to which way this path leads, even though natural English usually says where this path leads.

Because staza is the subject of the verb vodi.

• ova staza = nominative singular
• ovu stazu = accusative singular

Here, the path is the thing that leads, so it must be in the nominative: ova staza vodi = this path leads.

Also, staza is a feminine singular noun, so the demonstrative has to match it:

• masculine: ovaj
• feminine: ova
• neuter: ovo

So ova staza means this path.

Croatian often drops subject pronouns when the verb form already makes the subject clear.

• znam = I know
• ne znam = I don’t know

Because znam already shows 1st person singular, adding ja is usually unnecessary.

You could say Ja ne znam..., but that would usually add emphasis, like I don’t know....

Vodi is the 3rd person singular present tense of voditi.

Basic meanings of voditi include:

• to lead
• to guide
• to take
• to conduct

With roads, paths, stairs, and similar things, voditi often means to lead / to go in the sense of where something takes you.

So:

• Ova staza vodi... = This path leads...

This is very similar to English, where we also say This road leads to the village.

Because in this sentence the destination is expressed by kuda, not by a noun phrase.

With kuda, Croatian does not need a separate preposition like English to:

• Ne znam kuda ova staza vodi.
  = I don’t know where this path leads.

But if you name the destination with a noun, Croatian often uses do + genitive:

• Staza vodi do sela.
  = The path leads to the village.

So:

• kuda vodi = where/which way it leads
• vodi do + noun = leads to + noun

This is about aspect.

• padne is from the perfective verb pasti
• pada is from the imperfective verb padati

In kad padne mrak, the idea is when darkness falls / when it gets dark, meaning the moment that event happens. Croatian often uses the perfective present after kad for this kind of future or completed event.

So:

• kad padne mrak = when darkness falls / when it gets dark

If you used kad pada mrak, it would sound more like an ongoing or repeated process, and it is less natural here.

Croatian does not need a dummy subject like English it in this expression.

English says:

• it gets dark

Croatian often says:

• padne mrak
  literally: darkness falls

Here mrak is the actual subject of the verb.

So:

• mrak = darkness / dark
• padne mrak = darkness falls = it gets dark

That is why there is no separate word corresponding to English it.

Mrak is in the nominative singular.

That is because it is the subject of padne in the expression padne mrak.

So grammatically, the structure is:

• mrak padne = darkness falls

Even though English normally says it gets dark, Croatian builds this idea around the noun mrak.

Yes, both znam and vodi are present-tense forms, and padne is also formally a present form.

But in Croatian, present forms can be used in ways that English learners may find unusual:

• the ordinary present can describe a general fact
• the perfective present after words like kad often refers to a future event

So this sentence can mean something like:

• a general statement: I don’t know where this path leads when it gets dark
• or a future-oriented situation: I don’t know where this path leads once night falls

Context decides which reading is intended.

They mean the same thing here: when.

• kad = shorter, very common in everyday speech and writing
• kada = slightly fuller, sometimes a bit more formal or more emphatic

So you could also say:

• Ne znam kuda ova staza vodi kada padne mrak.

The meaning does not change.

No, Croatian word order is fairly flexible.

In an embedded question after ne znam, it is very natural for the question word kuda to come first:

• Ne znam kuda ova staza vodi.

But you may also hear:

• Ne znam kuda vodi ova staza.

Both are grammatical. The difference is mostly about style, rhythm, or slight emphasis, not basic meaning.

A direct question would also start with kuda:

• Kuda ova staza vodi?
• Kuda vodi ova staza?

So the key point is: kuda naturally introduces the embedded or direct question, while the rest of the sentence can move around more freely.