1. 首先，不是whats today，应该是What's the date?这个句子用于询问日期，回答的时候必须是某月某日。

2. 而what day is it today?询问的是日期，回答的是周几。

因此，这两个句子区别在于回答。看看下面例句:

What's the date? It's October 7th.

What day is it today? It's Friday.