The plan administrator for the 401(k) account is required to withhold 20% for federal income taxes.
You will receive a Form 1099-R from the plan administrator in January of 2020 for the withdrawal. The 1099-R is entered on your tax return, the taxable amount of the withdrawal is entered on your tax return as ordinary income and taxed at your current tax rate. The federal taxes withheld are entered on your tax return as a tax payment (just like from a W-2).
If you do not meet the age exceptions for the early withdrawal penalty then the 10% early withdrawal penalty will be assessed on your federal tax return and entered as a tax liability on the return.
