Are you asking: How do I stop a user right-clicking on a web page (made with Wordpress), so they do not see the menu that would normally appear after right-clicking on a web page?

With JavaScript you can capture the right click event and act on it. Depends what you want to do. Have it display a message, have it do nothing, or something else.

Out of curiosity, why do you want to disable it?

If you are trying to stop people viewing your source code, you are going to have to do more than disable right clicking on your site. There are tools such as cURL that let a user download the source code of a web page without even needing to use a web browser.