Metal atoms on graphene, when ionized, can act as a point charge impurity to probe a charge response of graphene with the Dirac cone band structure. To understand the microscopic physics of the metal-atom-induced charge and spin polarization in graphene, we present scanning tunneling spectroscopy (STS) simulations based on density functional theory calculations. We find that a Cs atom on graphene are fully ionized with a significant band bending feature in the STS, whereas the charge and magnetic states of Ba and La atoms on graphene appear to be complicated due to orbital hybridization and Coulomb interaction. By applying an external electric field, we observe changes in charge donations and spin magnetic moments of the metal adsorbates on graphene. ; Comment: 8 pages, 6 figures