I received a W2 from my employer as well as a 1099-MISC with my signing bonus. Now it is saying I have to fill out a form 8919. Why is this?

Form 8919 Uncollected Social Security and Medicare Tax on Wages is required to figure and report your share of the uncollected social security and Medicare taxes due on your signing bonus.  These taxes were not withheld by your employer when you received the bonus.

Thank you. So, it's asking if "the income on this Form 1099-MISC should have been included on Form W-2".  Is this asking whether it should have been taxed and thus put on the W2?

It's asking if the payment on the 1099 should have been considered wages, which it should have been.