Question words
The bare wh-words for what, who, when, why and how much; each opens a question on any topic.
nani
what
何 なに
Asks what; before d, t and n sounds it shortens to nan (nan da, nan desu ka, nan de), so you need both forms by ear.
kyou nani suru?
What are you doing today?
今日何する？
kyou wa nani suru n desu ka?
What are you doing today?
今日は何するんですか？
nani ga, nani o, but nan desu ka; the switch has to be automatic. nan no hanashi? = what are you talking about?
dare
polite donatawho
誰 だれ どなた
Asks who (dare ga), whose (dare no) or with whom (dare to); the answer takes ga.
dare ni kikeba ii?
Who should I ask?
誰に聞けばいい？
donata ni kikeba ii desu ka?
Who should I ask?
どなたに聞けばいいですか？
dare desu ka is fine with coworkers; donata is the softer choice with strangers and on the phone.
itsu
when
いつ
Asks when, and with kara or made asks since when or until when (itsu kara?, itsu made?).
itsu ga ii?
When's good for you?
いつがいい？
itsu ga ii desu ka?
When would suit you?
いつがいいですか？
No ni after itsu: itsu iku?, not itsu ni iku?
nande
polite doushitewhy
なんで どうして
The everyday casual 'why', said alone (e, nande?) or in a question ending in no?, and usually answered with kara; it can sound blunt or accusing, so doushite is softer and the safe choice in polite speech.
nande konakatta no?
Why didn't you come?
なんで来なかったの？
doushite konakatta n desu ka?
Why didn't you come?
どうして来なかったんですか？
By ear, nande iku? sounds the same whether it means 'why are you going?' or 'how are you getting there?', and is usually heard as 'why'; to ask for the route, say dou yatte iku? or nani de iku?
Learn first: nani
ikura
how much (price)
いくら
Asks a price or amount (kore ikura?); ikura demo means 'as much as you like' (ikura demo aru), and ikura -te mo means 'no matter how much' (ikura tabete mo futoranai).
zenbu de ikura?
How much is it altogether?
全部でいくら？
zenbu de ikura desu ka?
How much is it altogether?
全部でいくらですか？
ikura is for price and amount; for 'how many' the word is ikutsu.
Learn first: kore