Could you tell me at which branch they are recruiting?
At which branch are they looking for people to hire?
Which one of their branches are hiring?
ご質問ありがとうございます。
① "Could you tell me at which branch they are recruiting?"＝「どの店舗で募集しているのか教えてくれますか。」
② "At which branch are they looking for people to hire?"＝「どの店舗で採用する人々を探していますか。」
③ "Which one of their branches are hiring?"＝「（この会社のうち）どの店舗で採用していますか。」
ご参考に。
アメリカ合衆国 
