"Where" gets used a little differently in Japanese.
ゆみってどこが好き？ = lit.:Where do you like about Yumi?
Meaning: What do you like about her?
The first time someone asked me "where" I liked about my wife, I didn't know how to respond. When her friend saw I didn't under stand she offered some helpful Katakana/English: What are her charm points? チャームポイント. "Charm Points" confused me even more, I had no idea what she was trying to say.
どっか食べに行こう？ どこか gets shortened to どっか. It still means Let's go [somewhere] and eat?
Obviously, どっか is informal.