Which line item from Schedule A should I use to enter my state and local taxes withheld? Line 5a? 5d? or 7?
If you don't elect to deduct general sales taxes, you'll enter these on line 5a of Schedule A, and they’ll be totaled on line 5d.
According to Line 5a in the Instructions for Schedule A, you'll enter:
State and local income taxes withheld from your salary during 2020. Your Form(s) W-2 will show these amounts. Forms W-2G, 1099-G, 1099-R, 1099-MISC, and 1099-NEC may also show state and local income taxes withheld; however, don't include on line 5a any withheld taxes you deducted on other forms, such as Schedule C, E or F.
Please use the link above to learn what can be included on line 5a besides withholding.
In TurboTax, you enter your state and local withheld tax amounts when you enter your W-2. The information will then flow automatically to Line 5a of your Schedule A.