About 60% of all US income (GDI) is compensation for labor (salaries, wages, benefits), 40% compensation for capital (dividends, interest, rents). Both parts are already taxed, at varying rates. The total amount of taxation is about 33% of GDI, while total spending is about 36% (the deficits is filled by borrowing).
Since the entire article looks like a big tax and transfer proposal, it's pretty bizarre to omit almost all basic government accounting, except for a throwaway footnote. The analogy with joint-stock companies or Homestead acts are neither here nor there. The government owned a lot of American land back then. It doesn't not own a large share of of current American corporations, nor many laborers. So the way to pay any significant "citizen's dividend" is boring old taxes.
A much better discussion with concrete numbers and speculation on incentive effects can be found here: https://arstechnica.com/civis/viewtopic.php?f=24&t=1286141&s...