Z czym jesz naleśniki?

Because the preposition z (with) requires the instrumental case in this meaning.

The basic word co means what, but after z it changes form:

• co → czym

So:

• z czym = with what

This is very common in Polish: a preposition often changes the form of the noun or pronoun that follows it.

Czym is the instrumental singular form of co (what).

You can think of it like this:

• nominative: co = what
• instrumental: czym = with what / by what

So in this sentence, czym is used because z needs the instrumental.

Jesz is the 2nd person singular present-tense form of the verb jeść (to eat).

So it means:

• jesz = you eat / are eating

Polish verb endings usually show the subject clearly, so you do not need a separate word for you.

Because Polish usually omits subject pronouns when they are not needed.

The ending in jesz already tells you the subject is you (singular), so:

• Z czym jesz naleśniki? = natural
• Z czym ty jesz naleśniki? = possible, but more emphatic

Adding ty can sound like you are stressing you, for example in contrast with someone else.

Polish does not use an auxiliary like English do to make questions.

In English, you say:

• What do you eat pancakes with?

But in Polish, the main verb stays as it is:

• Z czym jesz naleśniki?

A question is shown by:

• the question word (z czym)
• intonation in speech
• punctuation in writing

So there is no separate equivalent of English question do here.

Because naleśniki is the direct object of jesz, so it is in the accusative plural.

The singular noun is:

• naleśnik = pancake / crêpe

Plural:

• nominative plural: naleśniki
• accusative plural: naleśniki

For masculine inanimate nouns like naleśnik, the accusative plural is the same as the nominative plural. That is why the form does not change.

It is plural.

• naleśnik = one pancake / crêpe
• naleśniki = pancakes / crêpes

So the sentence is asking about pancakes in general, not just one.

If you wanted the singular, you would say:

• Z czym jesz naleśnik? = What do you eat a pancake with?

Because Polish usually puts the question phrase near the beginning of the sentence.

So:

• Z czym jesz naleśniki? = the normal order

This is similar to English putting what first in a question.

Other word orders are possible in Polish, but they usually sound more marked, more conversational, or more emphatic.

It can mean either, depending on context.

Polish present tense often covers both:

• you eat (habitually / generally)
• you are eating (right now)

In this sentence, the most natural reading is usually general:

• What do you eat pancakes with?
• meaning What do you usually have with pancakes?

But in the right context, it could also refer to what someone is eating at the moment.

A natural answer usually uses z + instrumental again.

Examples:

• Z dżemem. = With jam.
• Z cukrem. = With sugar.
• Z serem. = With cheese.
• Z Nutellą. = With Nutella.
• Ze śmietaną. = With sour cream.

You can also make a full sentence:

• Jem naleśniki z dżemem. = I eat pancakes with jam.

Z sometimes becomes ze to make pronunciation easier.

For example:

• ze mną = with me
• ze śmietaną = with sour cream

But in this sentence, z czym is the normal form.

So you should learn z as the basic preposition, and ze as a pronunciation-based variant used in some combinations.

It is neutral and works well in everyday Polish.

Because it uses jesz, it is addressed to one person in the informal you form.

If you wanted to ask more formally or address someone as Pan/Pani, you would say:

• Z czym Pan je naleśniki?
• Z czym Pani je naleśniki?

Those mean What do you eat pancakes with? in a polite/formal way.