Your employer may not use a control number (box d) -- it is totally optional. An employer sometimes uses the control number to identify individual W-2 forms. The IRS does NOT require an employer to enter this, so it may be blank.
Turbo is asking me to put in control number from box d. I do not have a box d, for filing
A Control Number (box D) is used by many payroll departments to uniquely identify a W-2 in their system.
If your W-2 doesn't have one, box D can be left blank.
See this TurboTax Help.