Nevím, zda přijde.

I do not know whether he will come.

Breakdown of Nevím, zda přijde.

• vědět: to know
• přijít: to come
• zda: whether

Questions & Answers about Nevím, zda přijde.

Why is Nevím used instead of something like já nevím?

In Czech, the subject pronoun is often omitted because the verb ending already shows who the subject is.

• nevím = I don't know
• the ending -ím tells you it is I

So Nevím is the normal, natural way to say it.
You can add já for emphasis or contrast:

• Já nevím. = I don't know. / Me, I don't know.

In a neutral sentence, leaving out já is standard.

What does zda mean here?

zda introduces an indirect yes/no clause. In this sentence, it means something like whether or if.

So the structure is:

• Nevím = I don't know
• zda přijde = whether he/she/it will come

This is more formal or bookish than jestli, which is very common in everyday speech.

Can I say Nevím, jestli přijde instead?

Yes. That is very common and natural.

• Nevím, zda přijde.
• Nevím, jestli přijde.

Both mean the same thing here. The main difference is style:

• zda = a bit more formal, written, or careful
• jestli = very common in everyday spoken Czech

So as a learner, you will hear jestli a lot, but zda is absolutely correct.