Why do you ask?
It makes little difference in filing your tax return. One possibility: you may have too much social security tax withheld (if your total wages is over $137,700) and will have to include the refund request with your income tax filing.
You should ask the employer and see if you should be getting one or two W-2 forms so you don't miss one ... also look at the last pay stub ... is the YTD amounts reflect the entire year's income to date or only part of it ? That will give you a hint as to how many W-2 forms you will get.
new job for what purpose?
there are revenue procedures and letter rulings that allow the new company to be treated as a successor employer (in an asset purchase or merger where the required tests are met). the benefit to both you and it are that they get credit for the fica and medicare wages paid by the old employer and also those withheld from the employees' paychecks. the advantage is they save on fica(social security) and unemployment taxes. since your wages from the old employer count toward the max fica that can be withheld, there will be no excess fica for you to claim. you get 1 w-2 that's a combination of the wages paid and taxes withheld by both companies along with other items reported on w-2's.