Nie wiem, skąd ona bierze tyle energii, ale wiem, dokąd chce pojechać latem.

Because they express direction, not just location.

• skąd = from where
• dokąd = to where / where to
• gdzie = where in the sense of location

So:

• Nie wiem, skąd ona bierze tyle energii = I don’t know where she gets so much energy from
• ale wiem, dokąd chce pojechać = but I know where she wants to go

A quick contrast:

• Gdzie ona jest? = Where is she?
• Skąd ona jedzie? = Where is she coming from?
• Dokąd ona jedzie? = Where is she going?

Polish uses commas in both of those places for standard grammar reasons.

1. Nie wiem, skąd...
   The comma separates the main clause from a subordinate clause introduced by a question word like skąd, dokąd, co, kiedy, dlaczego, etc.

2. ..., ale wiem...
   The comma before ale is required because ale means but, and it joins two coordinate clauses.

So the structure is:

• Nie wiem, skąd ona bierze tyle energii,
• ale wiem, dokąd chce pojechać latem.

Yes, it could be omitted.

Polish often drops subject pronouns because the verb ending already tells you the person. Here, bierze means she/he/it takes/gets, so ona is not strictly necessary.

You could say:

• Nie wiem, skąd bierze tyle energii...

That would still be correct.

Including ona can:

• add emphasis,
• make the subject clearer,
• sound slightly more contrastive or expressive.

So ona is optional here, but natural.

Because Polish verb endings usually show the subject.

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

The implied subject is ja (I), but Polish usually leaves ja out unless it is needed for emphasis.

So:

• Nie wiem = I don’t know
• Ale wiem = But I know

This is very normal in Polish.

Because after quantity words like tyle (so much / that much / so many), the noun normally appears in the genitive.

So:

• energia = dictionary form, nominative
• energii = genitive

That is why Polish says:

• tyle energii = so much energy

Compare:

• mam energię = I have energy
• mam dużo energii = I have a lot of energy
• mam tyle energii = I have so much energy

So the quantifier changes the case.

Bierze is the 3rd person singular present tense of brać.

Basic meaning:

• brać = to take

But in this sentence, a more natural English translation is:

• to get
• to draw
• to find

So skąd ona bierze tyle energii literally is something like:

• from where does she take so much energy

But natural English is:

• where does she get so much energy from?

This is a very common kind of meaning shift between literal Polish and natural English.

This is mainly about aspect.

• jechać = imperfective, to go / travel (usually by vehicle), focusing more on the process
• pojechać = perfective, to go / set off / go somewhere successfully, focusing on a single completed trip

In this sentence, the speaker knows the destination she wants to go to, so a one-time, goal-directed trip is implied. That makes pojechać very natural.

• dokąd chce pojechać = where she wants to go

If you said chce jechać, it would feel more like emphasis on the act or process of traveling, not the completed trip to a destination.

Traditionally, yes: jechać / pojechać is connected with travel by some means of transport.

Very roughly:

• iść / pójść = go on foot
• jechać / pojechać = go by vehicle / travel

But in real everyday Polish, pojechać is also often used quite broadly for going somewhere, especially on a trip, vacation, or journey.

So in this sentence:

• dokąd chce pojechać latem

it sounds like:

• where she wants to go in the summer
• or more specifically, where she wants to travel/go off to in the summer

Latem is an adverbial use of the instrumental form of lato (summer).

So:

• lato = summer
• latem = in summer / during the summer

This is a very common time expression in Polish.

Similar examples:

• zimą = in winter
• wiosną = in spring
• jesienią = in autumn

So latem does not mean with summer here. It simply functions as a time expression: in the summer.

Polish word order is more flexible than English, but the version in the sentence is very natural.

Current sentence:

• Nie wiem, skąd ona bierze tyle energii, ale wiem, dokąd chce pojechać latem.

Possible variations:

• Nie wiem, skąd bierze tyle energii, ale wiem, dokąd chce pojechać latem.
• Dokąd chce pojechać latem, wiem, ale nie wiem, skąd ona bierze tyle energii.
  This is grammatical, but much less neutral.

Changing the order usually changes:

• emphasis,
• rhythm,
• style,
• what sounds most natural in context.

So yes, the order is somewhat flexible, but the original version is the best neutral choice.

Ale means but, and it introduces a contrast.

The contrast is:

• I don’t know one thing
• but I do know another thing

So:

• Nie wiem... ale wiem... = I don’t know... but I know...

It creates a clear opposition between lack of knowledge and knowledge.

They are not direct questions. They are indirect questions embedded inside a larger sentence.

Compare:

Direct questions:

• Skąd ona bierze tyle energii?
• Dokąd chce pojechać latem?

Indirect questions:

• Nie wiem, skąd ona bierze tyle energii.
• Wiem, dokąd chce pojechać latem.

Just like in English, indirect questions do not use the direct-question word order. Polish simply keeps normal clause order after skąd and dokąd.

A rough guide:

• skąd ≈ skont (with a nasal vowel before the final consonant)
• dokąd ≈ do-kont
• chce ≈ roughly htse or kh-tseh, depending on how detailed you want to be

A few useful notes:

• ą is a nasal vowel
• ó sounds like u
• ch sounds like a harsh h / kh
• cz sounds like English ch in chop
• but chc in chce creates a consonant cluster that English speakers often find awkward at first

You do not need perfect pronunciation immediately, but it helps to notice that skąd and dokąd both contain the nasal ą.