Form 8888, Allocation of Refund (Including Savings Bond Purchases) is automatically generated by TurboTax when you choose to receive your refund all or in part with Savings bonds. The program will file this automatically along with your tax return, so you do not have to mail in this form.
From the TurboTax FAQ: We'll give you the option to purchase bonds when you get to the How do you want your federal refund? screen (in the File section).
When you get to that screen, simply check the box at the very bottom, which says I would like to split my refund into more than one account OR I would like to purchase U.S. Series I Bonds for myself, my family, or someone else. Click Continue and follow the onscreen instructions.
Please see this link for more information: https://ttlc.intuit.com/replies/3301972
