Are you talking about box 12 or box 14 on the W-2?
Box 14 has more to do with state and local but it does not have a code K. it generally has no affect on your federal return.
Box 12 code K is 20% excise tax on excess golden parachute payments per IRS instructions.
Code K—20% excise tax on excess golden parachute payments (not applicable to Forms W-2AS, W-2CM, W-2GU, or W-2VI). If you made excess golden parachute payments to certain key corporate employees, report the 20% excise tax on these payments. If the excess payments are considered to be wages, report the 20% excise tax withheld as income tax withheld in box 2

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