grammar - Using "it's" vs. using "it is" at the end of a sentence

Why is it that the following sounds incorrect:

"Would she know where it's?"

But this sounds fine:

"Would she know where it is?"

Answer

Because you don't contract away a stressed syllable. It's counter to the very nature of contraction.

See also the answer to Is there some rule against ending a sentence with the contraction "It's"?