"You like cookies."
no. You only use "ty" whan talking with friends/family members etc.
the situation you described can have two or even three possible answers (because of the unique situation)
1) you talk with the shop assistant if he/she personally has cookies - (I would use it if there is only one person of staff) "czy ma pan ciasteczka" "czy ma pani ciasteczka?"
2) you talk with shop assistant, but treat them as one person of the stuff, and ask if they have cookies.
you can be mildly polite and use just plural you:
- czy macie ciasteczka ?
you can be a bit more polite and add -państwo:
- czy macie państwo ciasteczka?
- czy mają państwo ciasteczka?
"wy" is a bit less informal then "ty". It is used in speeches, and when talking with one employee when they represent the company.
And if you are confused, maybe the best way is to ask "czy są ciasteczka? "
Why wouldn't it be? It's the most direct translation, if you are talking to one person.
Oh, unless you mean 'ciastka'? Well, as I probably wrote already under every sentence about 'cookies', I don't understand why 'ciasteczka' was introduced as a translation, it's a diminutive form. 'ciastka' is a more common word.
I'm not sure what you mean. While of course plural "Lubicie ciasteczka" is also correct and accepted, the sentence has been put in the database as singular "Lubisz ciasteczka", so the audio only exists for that version. So I don't know at what moment here you'd have an occasion to hear (or not) the audio for "lubicie".