No entenc què he de fer.

In Catalan, basic verbal negation is formed by putting no directly before the conjugated verb:

No entenc = I don’t understand

Unlike English, Catalan does not need a separate auxiliary like do here. So you say No entenc, not something like Entenc no.

Entenc is the 1st person singular present tense of entendre (to understand).

So:

• entendre = to understand
• entenc = I understand

That is why the subject jo (I) is not necessary: the verb form already shows who the subject is.

Catalan often leaves out subject pronouns when they are clear from the verb ending. This is very normal.

So:

• (Jo) no entenc = I don’t understand
• (Jo) he de fer = I have to do

You can add jo for emphasis or contrast, but it is not required.

Here què means what.

It has an accent because it is an interrogative word introducing an embedded question: what I have to do. The accent helps distinguish it from que, which very often means that or functions as an unstressed connector.

So:

• què = what
• que = that / which / connector, depending on context

Because the whole sentence is not a direct question. It is a statement that contains an indirect question.

• Direct question: Què he de fer? = What do I have to do?
• Indirect question: No entenc què he de fer. = I don’t understand what I have to do.

Catalan uses question marks for direct questions, not for embedded ones like this.

He de fer is the structure haver de + infinitive, which expresses obligation or necessity: to have to, must.

Breakdown:

• he = I have
• de = part of the structure
• fer = do

So he de fer means I have to do or I must do.

Yes, it is the same verb, haver, but it is being used in a different construction.

• he menjat = I have eaten
  
  • here he is an auxiliary in the perfect tense
• he de fer = I have to do
  
  • here he de expresses obligation

So the form he is the same, but the grammar is different:

• haver + participle → perfect tense
• haver de + infinitive → obligation

Because in this sentence, the whole clause què he de fer acts as the object of entenc.

So Catalan is structured like:

No entenc [què he de fer].
= I don’t understand [what I have to do].

You do not need an extra pronoun. If you wanted to say I don’t understand it/that, referring back to something already mentioned, you could say:

No ho entenc.

Here ho is the pronoun meaning something like it/that.

Because Catalan normally uses a full clause after què here, with a conjugated verb:

• què he de fer = what I have to do

English sometimes allows a shorter structure like what to do, but Catalan usually expresses this idea with què + conjugated verb + de + infinitive when the subject is understood as part of the clause.

So què he de fer is the natural Catalan pattern.