You can proceed without a value in box D. If you are unable to import your W-2 into TurboTax Online without a box D, choose "Type it in myself" and input the information from your W-2.
You may also get an error when trying to e-file. If this occurs, type in a randomized number according to the specifications detailed in this Help Article, I have no box D or Control Number on my W-2: "enter any number in this format: 5 digits, space, 5 digits (for example, 12345 67890)."