From corporate profits, which should be rising from labor cost cutting? Ultimately if the pie is growing and accruing to a few organizations, then either we create new wealth transfer mechanisms (progressive tax codes being one such previous example) or become a feudal society, which will probably stagnate.
UBI would be pure deficit spending which would basically double it. Our interest is already the #2 federal outlay at $1 trillion (defense is #5 last I heard) and we're already in fiscal dominance. So the end result is UBI would trigger much higher inflation which would make those UBI checks worthless.
Cost of UBI: 3,420,000,000,000
Where is $3.5 trillion going to come from?