I have someone who is taking a distribution of their after-tax contributions and associated earnings. The earnings are included as taxable income, but I can't find guidance on whether there is a penalty tax on those earnings? Can anyone point me in the right direction? Thanks.

The 10% early withdrawal penalty is imposed on the amount of the distribution that is includible in income. Therefore, the taxable portion of the distribution (the earnings) will be subject to the penalty, unless an exemption applies.