Translation:Where is the bank's exit?
For anyone confused, どちら can mean both Which one? and Which way? in English.
Think of it as asking for a general direction (Which way…?). This works for both physical and intangible options (Which thing…?). It is essentially a polite way to ask Which <anything>…?.
When used as Which one…?, it's generally for when the are only two options.
リンゴと バナナと どちらがすきですか。(Out of apples and bananas, which do you like?).
きたは どちらですか。(Which way is north?).
スミスさんは どちらですか。(Which one is Mr. Smith?)
It accepted the kanji 出口, but not the kanji 銀行. Duolingo is being ridiculous!