My 2016 state tax return was audited and determined that I owed more tax that year, but I was only notified of the tax owed in 2019, which paid in December of 2019. What is the correct way to report this payment if (a) I itemize in 2019, or (b) I take the standard deduction. I don't know which way I will end up going, but probably (a). I did itemize my deductions in 2016.
You can enter it as a itemized deduction on your 2019 federal return if you itemize. But since the Standard Deduction has increase so much more people take the Standard Ded now. And the State Tax Paid deduction is also limited. There is a limit on SALT deductions. SALT is State And Local Tax. Which includes property tax, any state tax paid like for last year’s return and includes any state withholding from your W2s and any 1099s you have. And any other taxes like in W2 box 14 & 19. You can only deduct up to 10,000 (5,000 MFS) for SALT State and Local Taxes.
If you take the Standard Deduction you don't need to enter it. It doesn't matter what you did in 2016.