There is generally no isolated entry place, in TT, for "withholding". The withholding entry is associated with the income. So, it depends on the source of the income and what kind of IRS document (W-2, 1099 etc) was used to make the entry.
That said, see @DianeW777 reply for the "last resort" place to enter withholding. The most common use for this place is state income tax withheld at a real estate sale closing.
