Saya heran kenapa dia diam-diam membawa novel itu ke kelas tanpa memberi tahu siapa pun.

I wonder why he/she secretly brought that novel to class without telling anyone.

Breakdown of Saya heran kenapa dia diam-diam membawa novel itu ke kelas tanpa memberi tahu siapa pun.

• itu: that
• saya: I
• dia: he/she
• ke: to

Questions & Answers about Saya heran kenapa dia diam-diam membawa novel itu ke kelas tanpa memberi tahu siapa pun.

What does Saya heran mean here? Is it literally I am surprised?

Yes, saya heran literally means I am surprised or I am puzzled. In this sentence, it is very natural to translate it as I wonder or I’m puzzled.

So:

• Saya heran = I’m surprised / puzzled / I wonder
• Saya heran kenapa... = I wonder why...

In Indonesian, heran often expresses puzzlement, not only shock.

Why is kenapa used here? Could it also be mengapa?

Yes. Kenapa and mengapa both mean why.

The difference is mainly tone and style:

• kenapa = more common in everyday speech
• mengapa = a bit more formal or literary

So this sentence could also be:

• Saya heran mengapa dia diam-diam membawa novel itu ke kelas tanpa memberi tahu siapa pun.

That would mean the same thing, just with a slightly more formal feel.

Why is there no word for that, like in I’m surprised that...?