How can I find net charge of an element?

Subtract the number of electrons from the number of protons.

In an atom, each proton has a charge of +1, each electron a charge of -1, and each neutron has no charge. If there's one more proton than electron, the overall charge is +1. An example of this is a sodium ion. The ion has 11 protons, but only 10 electrons, so 11-10 = +1.