How much training does a person need to be a Police officer?

That is determined entirely by agency or state regulating authority policy.

(in the US) All agencies will require a MINIMUM of a High School Diploma (or GED equivelant). A small number of agencies require a certain amount of college but the best thing to do would be to contact the agency you are interested in and ask.

Larger departments will probably have recruiting offices and the larger the department the more likely it is to have a website that will publish this very information.