What is the penalty for cashing out a 529K plan and not using the funds for education purposes?

The penalty for withdrawing 529 funds for non-qualified expenses is 10% of earnings, plus income tax on those earnings.

You will receive a form 1099-Q, for the distribution, from the 529 account.  Box 1 will be the total distribution amount. Box 2 will be the taxable "earnings".  That amount will have tax calculated on it.  In addition, there will be a penalty of 10% of the box 2 amount (identified on form 5329 as "additional tax".