Kagi is in katekana? Is it from another language?
It's a native Japanese word and it has a kanji 鍵 but it's complicated so for emphasis it's sometimes written in katakana. You will see it both ways in Japan.
確に that kanji is tough to learn. RPG Maker games helped me a lot though.
車のカギわどこ? wasnt accepted. It just gets more and more strict the further you progress
The particle needs to be written は, not わ. Even so, your sentence seems overly casual.