arimasuka: In English it's like 'Do you have ~~?' or 'Is there~~?' We use this phrase for things. For example, at a shop you ask a sales cleark, ' Sushi wa arimasuka?'
imasuka: 'Is ~~ there?' We use this for a person. For example, on the phone, you ask 'Jane wa imasuka?'
desuka: When you ask something, we put 'desuka?' at the end of a sentence. 'Tofu desuka?'