Nawet kiedy jestem zmęczony, czytam jeszcze jeden rozdział książki.

Polish usually drops subject pronouns when the verb already shows who is doing the action.

• jestem = I am
• czytam = I read / I am reading

So ja is not necessary. You could say Ja nawet kiedy jestem zmęczony..., but that would add emphasis, something like As for me... or I, even when I’m tired....

Nawet kiedy means even when.

• nawet = even
• kiedy = when

Together, they introduce a contrast: despite being tired, the person still reads another chapter.

Very close alternatives are:

• Nawet gdy jestem zmęczony...
• Nawet jeśli jestem zmęczony... = Even if I’m tired...
  This one is slightly more hypothetical.

In your sentence, nawet kiedy is very natural.

Because zmęczony agrees with the speaker in gender and number.

Here:

• jestem zmęczony = said by a man
• jestem zmęczona = said by a woman

Polish adjectives change form depending on who they describe.

So this sentence assumes the speaker is male. If the speaker is female, the sentence would be:

Nawet kiedy jestem zmęczona, czytam jeszcze jeden rozdział książki.

Yes. In this sentence, zmęczony is in the nominative singular masculine form.

After być (to be), predicate adjectives are normally in the nominative:

• Jestem zmęczony = I am tired
• Jestem gotowy = I am ready
• Jestem szczęśliwy = I am happy

So zmęczony matches the implied subject I.

Because nawet kiedy jestem zmęczony is a subordinate clause, and in Polish subordinate clauses are generally separated by a comma.

So:

• Nawet kiedy jestem zmęczony, czytam...

This is standard Polish punctuation.

Jeszcze jeden means one more, another one, or yet another.

• jeszcze = still / yet / more
• jeden = one

In this sentence, it means the speaker reads one more chapter.

Examples:

• Jeszcze jedna kawa. = One more coffee.
• Jeszcze jeden dzień. = One more day.
• Czytam jeszcze jeden rozdział. = I’m reading one more chapter.

Because Polish uses the genitive after a noun like chapter when you mean a chapter of a book.

• rozdział = chapter
• książki = of a book

So:

• rozdział książki = a chapter of a book

This is a very common Polish pattern:

• filiżanka herbaty = a cup of tea
• koniec filmu = the end of the film
• kolor domu = the color of the house

In this sentence, książki is genitive singular, meaning of a book.

That form happens to look the same as nominative plural for some nouns, but here the meaning and structure make it clearly genitive singular:

• rozdział książki = chapter of a book

If it were plural, it would mean chapter of books, which would not fit the sentence naturally.

Because czytam is imperfective, and it fits a repeated or habitual action well.

• czytam = I read / I am reading
• przeczytam = I will read / I will finish reading

Your sentence describes a general habit:

Even when I’m tired, I read one more chapter of a book.

So czytam is the natural choice.

If you said przeczytam jeszcze jeden rozdział, that would sound more like a single completed future action:

I will read one more chapter.

It can mean either, depending on context. Polish present tense often covers both English meanings.

• czytam = I read / I am reading

In your sentence, because it sounds like a general pattern or habit, the best English meaning is usually:

I read one more chapter

But in another context, czytam could mean I’m reading.

No, Polish word order is fairly flexible, though some versions sound more natural than others.

Your sentence is very natural:

Nawet kiedy jestem zmęczony, czytam jeszcze jeden rozdział książki.

Other possible versions:

• Czytam jeszcze jeden rozdział książki, nawet kiedy jestem zmęczony.
• Nawet kiedy jestem zmęczony, jeszcze czytam jeden rozdział książki.
  This is possible, but less natural in neutral speech.

Word order in Polish often changes the focus or emphasis, not the basic meaning.

Yes. Gdy and kiedy can both mean when.

So you can say:

• Nawet kiedy jestem zmęczony...
• Nawet gdy jestem zmęczony...

Both are correct. Gdy can sound a little more formal or literary in some contexts, but both are common.

Literally, rozdział książki means a chapter of a book. Without more context, it sounds fairly general.

In natural English, the sentence may be translated more generally as:

Even when I’m tired, I read one more chapter of my book / of a book.

Polish often leaves things less explicit if the meaning is already clear from context.

Only the adjective would need to change:

• masculine: Nawet kiedy jestem zmęczony, czytam jeszcze jeden rozdział książki.
• feminine: Nawet kiedy jestem zmęczona, czytam jeszcze jeden rozdział książki.

This is because Polish adjectives agree with the gender of the person speaking.

It is very close in meaning, but nawet kiedy most directly means even when, not even if.

• nawet kiedy = even when
• nawet jeśli / nawet jeśli jestem zmęczony = even if I’m tired

In many real situations, the difference is small, but grammatically the sentence you gave is best understood as even when.