You can read the bill here yourself - the lawyer speak may put you to sleep (and 880 pages :oops:.)
As far as knowing? - Read the bill - It is also summarized in the site below. It's clear if you make more than $75K (single) or $150K(married) according to your taxes in 2020 you will have to pay some back. If not, then you will not pay anything back. This is similar to the check we received in 2008 from the Bush admin during the great recession. BTW - this still needs to pass through the House of Representatives, which has a democratic majority vs the republican senate and president - so it is not finalized yet.
Washington Post Stimulus Check Calculator