How many electrons do two atoms in a double covalent bond share?

Four

Explanation - Covalent bonding occurs when electrons are shared between atoms. Double and triple covalent bonds occur when four or six electrons are shared between two atoms, and they are indicated in Lewis structures by drawing two or three lines connecting one atom to another.

Two atoms having a double covalent bond

share 2 electrons each.

for example, H-H

each hydrogen atom shares one electron with another hydrogen atom to attain helium configuration or the nearest noble gas configuration.