Is it a 401K? No, if it's on your W2 and is deducted from your pay it is already reported so do not enter it again under Deductions. You only can deduct Traditional IRA contributions you make outside of work. A 401k should be on your W2 in box 12 and has already been deducted from the wages in W2 box 1 and you can't deduct it again.
