Where; asks about a place or location.
すみません、トイレはどこですか？
Excuse me, where is the restroom?
彼は今どこにいるの？
Where is he right now?
ここから駅までどこくらいかかりますか？
How long does it take from here to the station?
どこで日本語を勉強しましたか？
Where did you study Japanese?
Used to ask about extent or degree — how far, how much; sometimes more literary/old-fashioned.
この問題がどこまで広がるかは分からない。
I don't know how far this problem will spread.
彼の熱意がどこまで続くか見てみよう。
Let's see how long his enthusiasm lasts (to what extent it continues).