I asked the library clerk about the loan period for the book.

我向图书馆员询问了这本书的借阅期限。

I asked her what the loan period was for the book.

我问她这本书的借期是什么时候。

The " loan period" is how long you can keep the book before you have to bring it back.

“借阅期”是指在您必须将书带回之前您可以保留该书的时间。

The " due (due) date" is the date that you have to bring it back, the date that the loan period ends.

“到期（到期）日期” 是您必须将其取回的日期，即贷款期限结束的日期。