Nie wiem, co zrobić z drugim pojemnikiem, bo szafka jest już pełna.

Polish often drops subject pronouns because the verb ending already shows who is doing the action.

• wiem = I know
• nie wiem = I don’t know

So ja is unnecessary here. You could say Ja nie wiem, but that usually adds emphasis, like I don’t know.

Because co zrobić z drugim pojemnikiem is a subordinate clause: literally, I don’t know what to do with the second container.

In Polish, subordinate clauses are normally separated by commas, so:

• Nie wiem, co zrobić...

There is also a comma before bo, because bo introduces another clause:

• ..., bo szafka jest już pełna

This is about aspect, which is very important in Polish verbs.

• zrobić = perfective, meaning a completed action
• robić = imperfective, meaning an ongoing, repeated, or general action

In Nie wiem, co zrobić..., the speaker is looking for a concrete solution in this specific situation, so zrobić is the natural choice: what to do / what should I do now.

If you said co robić, it would sound more like:

• what to be doing
• what one usually does
• what to do in general / repeatedly

This is a very common Polish pattern meaning what to do with ...

So:

• co zrobić z drugim pojemnikiem = what to do with the second container

The preposition z here is part of the whole expression. It does not mean from here; it means something closer to with.

Because after z in this meaning, Polish uses the instrumental case.

Base form:

• pojemnik = container

Instrumental singular:

• pojemnikiem

So:

• z pojemnikiem = with the container
• z drugim pojemnikiem = with the second container

Adjectives in Polish must agree with the noun in:

• gender
• number
• case

Since pojemnikiem is masculine singular instrumental, the adjective must also be masculine singular instrumental:

• drugi pojemnik = nominative
• z drugim pojemnikiem = instrumental

That is why you see drugim, not drugi.

Usually yes: drugi normally means second.

So z drugim pojemnikiem most naturally means with the second container.

In some contexts, Polish can use drugi in a looser way, a bit like the other one, but if you want to say another/different, words like inny are often clearer.

Because pełna must agree with szafka.

• szafka is feminine singular
• therefore the adjective must be feminine singular too: pełna

Compare:

• pojemnik jest pełny — the container is full
• szafka jest pełna — the cabinet is full
• pudełko jest pełne — the box is full

In the present tense, Polish normally uses jest in sentences like this:

• szafka jest pełna = the cabinet is full

In casual speech, people sometimes drop jest, especially in very informal contexts, but the full standard sentence keeps it.

So here jest is the normal, correct choice.

już means already.

So:

• szafka jest pełna = the cabinet is full
• szafka jest już pełna = the cabinet is already full

It adds the idea that the cupboard has reached capacity by now, so there is no more room. It helps explain why the speaker has a problem with the second container.

Both can mean because, but they have different styles.

• bo = everyday, conversational, very common
• ponieważ = a bit more formal or neutral
• gdyż = more formal/written

In this sentence, bo sounds natural and ordinary:

• ..., bo szafka jest już pełna.

Not exactly.

• szafa usually means a larger wardrobe or cabinet
• szafka is smaller: a cupboard, cabinet, little cabinet, bedside cabinet, etc.

In a kitchen, szafka often means a cupboard or cabinet. So here it suggests some smaller storage space that is already full.

Yes. That is also very natural.

• Nie wiem, co zrobić... = I don’t know what to do...
• Nie wiem, co mam zrobić... = I don’t know what I’m supposed to do / what I should do...

The version with mam is a bit more explicit. The original sentence is shorter and very idiomatic.

Not completely. Polish word order is fairly flexible, though some orders sound more neutral than others.

The original sentence is neutral and natural:

• Nie wiem, co zrobić z drugim pojemnikiem, bo szafka jest już pełna.

You could move parts around for emphasis, for example:

• Z drugim pojemnikiem nie wiem, co zrobić...

But that sounds more marked, because it emphasizes the second container. The original order is what learners should probably use first.