what's today?与What day is today? 与What's the date?三者有什么区别?

what day is today是问星期几
what's the date是问几号

what day is today是问星期几
what's the date是问几号
what's today是问几月几日星期几

一般不会有what's today?的问法，这句话的字面意思是“今天是什么”，大概属于比较文学化的语言
What day is today? 是问星期几的，比如回答可以是Today is Wednesday.
What's the date (today)?是问几号的，比如回答可以是It's December 3rd.

what day is （it） today? 是问星期几
what's the date today? 是问日期