John Gill Commentary Leviticus 20:9

"For every one that curseth his father or his mother shall surely be put to death: he hath cursed his father or his mother; his blood shall be upon him." — Leviticus 20:9 (ASV)

For everyone that curseth his father or his mother
Here begins the account of the penalties annexed to the several laws in the preceding chapter; and that respecting the fear and honour of parents being the first, (Leviticus 19:3) , is here begun with:

shall surely be put to death ;
the Targum of Jonathan adds, "by casting of stones," stoning being the punishment of such transgressors:

he has cursed his father or his mother :
to do either is his sin, and a capital crime it is:

his blood [shall be] upon him :
he shall be guilty of death, be condemned unto it, and punished with it, namely, by stoning; for, as Jarchi observes, wherever it is, "his blood [shall be] on him", or "their blood shall be on them", it is to be understood of stoning.