How do I report on turbo tax a 1042s with code 28 and federal tax withheld?

If you have a 1042-S with code 28 related to casino winnings and federal income taxes were withheld, you will need to enter this information in 2 separate places. One will be the entry for the amount of winnings and the other will be for the federal income taxes withheld.

For the winnings from the 1042-S -

To enter a gambling winnings in TurboTax, log into your tax return (for TurboTax Online sign-in, click Here and click on "Take me to my return") type "gambling income not on w-2g" in the search bar then select "jump to gambling income not on w-2g". TurboTax will guide you in entering this information.

To enter the withholdings reported on the 1042-S -

Once you have signed into your TurboTax Account (for TurboTax Online sign-in, click Here), select "Take Me To My Return" and type "estimated tax payments" in the search bar then select "jump to estimated tax payments". This will take you to the Other Income Taxes section 

Alternatively, to enter your state income taxes in TurboTax Online or Desktop, please follow these steps:

1. Once you are in your tax return, click on the “Federal Taxes” tab ("Personal" tab in TurboTax Home & Business)
2. Next click on “Deductions & Credits”
3. Next click on "jump to full list" or “I’ll choose what I work on”
4. Scroll down the screen until to come to the section “Estimates and Other Taxes Paid ”
5. Select "Other Income Taxes" and start (or update).
6. Scroll down to "withholding not already entered on a W-2 or 1099"
7. Enter the 1042-S withholdings in the federal amounts box.

Yes this is correct.  Box 1 is the income code.

Here is a link to the sample Form and explanation:   FORM 1042-S