also: どしたの
what's the matter?; what's wrong?
Casual expression used to ask someone why they look upset, worried, or are acting strangely. Often used when noticing a change in someone's mood or behavior.
You look pale. What's wrong?
what happened to ...?; where is ...?
Used with a noun marked by は or を to ask about the whereabouts or state of something or someone. Often implies surprise or concern that the thing is missing or different.
Huh? What happened to your wallet?
You suddenly went quiet. What's the matter?
昨日買った本をどうしたの？
What did you do with the book you bought yesterday?