On your website, every single page includes a footer. In most cases, you will see that your contact information is on the left here, and on the right you usually see useful links. See below:

The footer of your website is completely customizable; and one of the widgets you can add here is testimonials. This means on every page of your website you can ensure a random testimonial is displayed.  See below:

The best part is, setting this up only literally takes a few seconds to do! Watch the video below to learn exactly how: