Here's an approach to help you decide how to fill out your W-4 forms:
- New Job's W-4: Since you're leaving your current job in two weeks, fill out the W-4 for your new job as if you have only one job. This will ensure accurate withholding based on your new employment
- Current Job's W-4: You don't need to update the W-4 for your current job since you're leaving soon. Your current employer will continue withholding based on your existing W-4 until you leave.
To help ensure your withholding is where it needs to be and reduce the likelihood of owing money to the IRS, you can use the the TurboTax W-4 Calculator to estimate your withholding.
See this TurboTax Article on changing jobs and tax forms