Under the employer name and address. But you don't need it. See
https://ttlc.intuit.com/community/forms/help/i-have-no-box-d-or-control-number-on-my-w-2/00/26469
The control number in box d is not required by the IRS - it is used by your employer. As a result, if it causing you trouble, just delete it. If it is not causing you trouble, then leave it in - it won't matter.
