Nowhere since dead people don’t tend to collect Social Security benefits.

Was this back pay for a claim that lingered in court for years?  I've often wondered whether those claims evaporate at death.  

If it does belong on the 1041 I suggest other income.

What happens when a claimant dies and there is an SSD application pending? Can a family member still receive  SSD benefits on behalf of the deceased? The answer is yes.

An SSDI claim doesn’t die with the claimant. SSDI claims are also known as Title II claims. Social Security may decide even after a person has died that he or she should have been paid monthly SSDI benefits before death. SSA calls this situation an “underpayment.” The following list shows the order that the SSA uses when they pay out benefits. It shows who may collect an SSDI underpayment:

• a surviving spouse who was living with the disabled person, or who was entitled to SSDI benefits on the person’s record, during the month of death
• any child or children entitled to benefits on the deceased person’s record during the month of death, and
• any parents of the decedent entitled to benefits on the deceased person’s record during the month of death.

If none of the above relatives are alive, the SSD benefits will go to any surviving spouse, child, or parent, who doesn’t qualify under the above rules. Otherwise, the payments flow to the estate of the deceased.

https://cannondisability.com/blog/if-claimant-dies-can-family-get-ssd-benefits/

So it's income in respect of decedent, and those rules should apply.  It could have been not taxable, partially taxable, or 85% taxable to the decedent.  The estate should pay on the same amount.