Which is the correct response to someone if they want you to do this?
'Could you please do this' is most appropriate if you're politely asking someone to do something.
Can you do this... can also mean like you're asking if they can do the job or not. You can change it to 'Can you do this for me,' to clear the confusion.
Can you please do this... is okay, too, because the word 'please' automatically tells us that you're requesting someone to do something.