The Box D Control Number is a code that identifies your unique W-2 form in your employer's records. This number is assigned by the company's payroll processing software. You can find it on your copy of the W2. I have included a screenshot of a sample W2 below. It is necessary for the import feature to work. But, if your W2 does not contain one follow the guidance in the TurboTax FAQ below -
https://ttlc.intuit.com/replies/4417180
