Answer:
both bonding electrons come from the oxygen atom
Step-by-step explanation:
A coordinate covalent bond is said to be formed when an electron pair is donated into a empty orbital of an atom from a filled orbital of another atom.
In this type of covalent bond, the shared electron pair is furnished by only one of the bonding species.
The bonding between H^+ and H2O to form H3O^+ involves donation of a lone pair of electrons on oxygen into the empty 1s orbital of H^+ hence the two bonding electrons come from oxygen. This is why the bond is called a coordinate covalent bond.