So after much tearing of hair and gnashing of teeth, I think my solution is: Gross Income Sourced at the Beneficiary Level is the amount reported on Schedule K-1 in Box 14 with Code E. I realize that is described as "net investment income" but it's a gross number from the beneficiary's standpoint.
To get foreign source income, I reverse-engineered (correctly, I hope) how Turbotax computed the other amounts on the beneficiary's Schedule K-1. The key (for me, at least) is that Turbotax allocates certain "attorney, accountant and return preparer fees" reported on line 14 of the Trust's Form 1041 to some, but not all, income items in arriving at the income distributed to beneficiaries. Here, the entire amount on line 14 was allocated to "Interest Income" (Form 1041, line 1) and "Total Ordinary Dividends" (Form 1041, line 2a), specifically to non-qualified dividends.
The Trust's foreign source income included both qualified and non-qualified dividends. I divided the Trust's foreign non-qualified dividends by the sum of the Trust's interest income and all non-qualified dividends to arrive at the percentage of the Trust's "attorney accountant and return preparer fees" allocated to foreign source income. I multiplied the total "attorney accountant and return preparer fees" by this percentage and subtracted the result from the Trust's foreign source income to arrive at the "Gross Income Sourced at Beneficiary Level: Foreign Source Income." "Gross Income Sourced at Beneficiary Level: U.S. Source Income" is then "Gross Income Sourced at Beneficiary Level" (Box 14, Code E) minus "Gross Income Sourced at Beneficiary Level: Foreign Source Income." These results are for the amounts distributed to all beneficiaries. Multiply them by the beneficiary's general allocation percentage to get the beneficiary's foreign tax credit .
I had expected the "attorney accountant and return preparer fees" to be allocated ratably across all the income income items reported on the beneficiary's Schedule K-1, rather than just interest income and non-qualified dividends. But it turns out that the Instructions for Form 1041 and Schedules A, B, G, J, and K-1 (2024) state: "deductions that aren't directly attributable to a specific class of income may generally be allocated to any class of income, as long as a reasonable portion is allocated to any tax-exempt income."
