Perusing the Wikipedia page for the Laffer Curve (https://en.wikipedia.org/wiki/Laffer_curve), it seems that most studies find we could double our current tax rates and still be on the left of the peak (65%-70%). Given that our current federal revenue is appr. $3.5 trillion, it seems we could afford Yang's $2.8 trillion in UBI without issue.

Source for UBI total cost: https://freedom-dividend.com/ note: I ignored his ~$0.9 trillion in predicted savings/economic growth but that would lessen the bill even more.