Hi Roz, 

this setting is not available out-of-the-box, so custom code is needed:

the js code responsible for testimonials is located in the file /wp-content/themes/thegem/js/testimonials-carousel.js

To display the testimonials in a random order, you need to shuffle the elements before initializing the carousel. You can achieve this by modifying the jQuery code to shuffle the .gem-testimonial-item elements.

You need to add the following code: 

// Shuffle testimonials
$testimonials.sort(function() {
return 0.5 - Math.random();
}).appendTo($testimonialsCarousel);

here: 

The only thing is that this change should be done via the child theme in order to avoid problems with the future theme updates (the file will be overwritten in the parent theme). I would suggest that you give a try to this code and if everything is working as expected - let me know so we can consider the way to isolate this customization via the child theme. 

Hi Roz, 

will add this to the devs list, hopefully it will be covered in the next release.