Dutch question words (vraagwoorden) include: wie (who — for people), wat (what — for things), waar (where), wanneer (when), hoe (how), waarom (why), welk/welke (which — de-word: welke, het-word: welk), hoeveel (how much/many), hoe lang (how long — time), hoe ver (how far), hoe oud (how old), hoe laat (what time — literally how late). These trigger V2 word order in main clause questions.
Question formation: the question word takes position 1, the finite verb takes position 2, and the subject follows: Waar woont hij? (Where does he live? — waar / woont / hij). Wat eet je? (What are you eating? — wat / eet / je). Waarom lach je? (Why are you laughing? — waarom / lach / je). When the question word is itself the subject, normal word order follows: Wie werkt hier? (Who works here? — wie is subject). Wat is er gebeurd? (What has happened? — wat is subject).
Compound question words with waar: these are used when asking about things (not people) with a preposition. Waar + preposition (when preposition starts with a vowel, waar + r + preposition): waarover (about what), waarvoor (for what), waarmee (with what), waaraan (on/at what), waarvan (of what), waarbij (at which/where). Example: Waarover praat je? (What are you talking about?). Compare: Over wie praat je? (Who are you talking about? — person, so use pronoun + preposition, not waar-compound).