Sure thing; that's out of
An Update to the Budget and Economic Outlook: 2024 to 2034 (dated June 2024) which was put out by the Congressional Budget Office. Search that document for the heading "The Budget Outlook, by Fiscal Year".
Elon Musk was advertising that he'd
cut $2 trillion from the budget. But if you look at the discretionary spending for the years 2023, 2034 and 2035 in that chart, you'll see that he doesn't have any more than $1.832 trillion in discretionary spending in any of those years to cut from. So I'm guessing he's not really talking about cutting $2 trillion from a single year; and is instead going by the old standby of cutting $2 trillion from the budget over the next decade (with the bulk of the cuts being in years 8 through 10 - which, of course, we'll never see).