Learn Hardcore Indonesian: Dia menanyakan waktu presentasi kepada guru di perpustakaan. - He/She asks the teacher about the presentation time in the library.

Menanyakan is transitive and takes the thing being asked as its direct object: pattern = menanyakan + [thing] + kepada + [person]. Example: Dia menanyakan waktu presentasi kepada guru.
Bertanya is intransitive; you typically add a preposition for the topic: pattern = bertanya (kepada + person) (tentang/soal + thing). Example: Dia bertanya kepada guru tentang waktu presentasi.
Both are correct; menanyakan sounds a bit more formal and compact when the focus is the information requested.

Why is kepada used? Can I use ke, pada, or sama instead?

Kepada is the standard preposition for a human recipient: menanyakan sesuatu kepada seseorang.
Pada can also be used with people (often formal/written): bertanya pada guru.
Ke literally marks direction, but in everyday speech people often say nanya ke guru; it’s informal.
Sama is very casual colloquial: nanya sama guru. Avoid sama in formal contexts.

What exactly does di perpustakaan modify here? The teacher, the act of asking, or the presentation?

As written, it’s ambiguous and could mean: 1) The asking happened at the library: “asked … at the library.” 2) The teacher was in the library: “asked the teacher who is in the library.” 3) The presentation is in the library: “asked the time of the presentation that’s in the library.” To disambiguate:

Action location: Di perpustakaan, dia menanyakan waktu presentasi kepada guru.
Teacher’s location: Dia menanyakan waktu presentasi kepada guru yang ada di perpustakaan.
Presentation’s location: Dia menanyakan waktu presentasi yang diadakan di perpustakaan kepada guru.

Is menanyakan tentang acceptable, like “menanyakan tentang waktu presentasi”?

Better avoid it in formal Indonesian. With menanyakan, the object already expresses the topic, so tentang is redundant. Prefer:

Dia menanyakan waktu presentasi (kepada guru). If you want tentang, use bertanya:
Dia bertanya kepada guru tentang waktu presentasi.

Could I use menanyai instead of menanyakan?

Yes, but the meaning shifts:

Menanyai targets the person as the direct object (often suggests repeated or detailed questioning): Dia menanyai guru tentang waktu presentasi.
Menanyakan targets the information as the direct object: Dia menanyakan waktu presentasi kepada guru. Choose based on whether you want to highlight the person questioned (menanyai) or the information sought (menanyakan).

How would people say this more casually in everyday speech?

Dia nanya waktu presentasi ke/sama guru di perpus. (Perpus = slang for perpustakaan)
Or even: Dia nanya, “Jam berapa presentasinya?” ke guru.

How can I make it more polite or formal?

Ia menanyakan waktu presentasi kepada guru di perpustakaan. (Ia is more formal)
With polite framing: Permisi, Bu/Pak, saya ingin menanyakan waktu presentasi.
Referring to a respected third person: Beliau menanyakan waktu presentasi kepada guru.

Does Dia mean “he” or “she”?

Dia is gender-neutral and can mean he or she. Alternatives:

Ia: more formal/literary, typically as a subject.
Beliau: respectful he/she (for elders or esteemed people). Note: dia is usually lowercase unless at the start of a sentence.

Is waktu presentasi the best phrase? What about jam, jadwal, or kapan?

Waktu presentasi: general “the time of the presentation.”
Jam/pukul presentasi: specific clock time (use pukul in formal, jam in everyday speech).
Jadwal presentasi: the schedule (could include date, time, order).
Kapan presentasinya?: a direct question (“When is the presentation?”). Choose based on how specific you want to be.

How do I express past, ongoing, or future in Indonesian with this sentence?

Indonesian has no tense inflection; add time words:

Past: Tadi dia menanyakan… / Kemarin dia menanyakan…
Completed: Dia sudah menanyakan…
Ongoing: Dia sedang menanyakan…
Future: Dia akan menanyakan… / Nanti dia akan menanyakan…

Can I move di perpustakaan earlier in the sentence?

Yes:

Di perpustakaan, dia menanyakan waktu presentasi kepada guru. (clearly the place of the asking) To attach it to the presentation or the teacher, use a relative clause:
…waktu presentasi yang diadakan di perpustakaan…
…kepada guru yang ada di perpustakaan.

How do I use the -nya clitic here (definiteness and pronouns)?

waktu presentasinya = “the time of the (known) presentation.”
Dia menanyakannya kepada guru. = “He/She asked about it…” (-nya refers to previously mentioned info).
kepadanya = “to him/her.”
gurunya = “his/her teacher” or “the (specific) teacher,” depending on context.

What are the passive alternatives?

Focus on the information: Waktu presentasi ditanyakannya kepada guru di perpustakaan.
Focus on the teacher: Guru di perpustakaan ditanyai soal waktu presentasi.
Colloquial passive: Guru di perpustakaan ditanya tentang waktu presentasi.

Is kepada required with menanyakan if I mention the person?

Yes. With menanyakan, the person asked is introduced by kepada (or informal ke/sama). You cannot say Dia menanyakan guru…. If you want the person as the direct object, switch to menanyai: Dia menanyai guru….

Why di perpustakaan and not ke perpustakaan?

Di marks location (at/in): di perpustakaan = “at the library.”
Ke marks movement toward: ke perpustakaan = “to the library.” Here you’re describing where the asking happened, so di is correct.