there are many ways to solve 'related' stuff.
In your case, can't you just have a subfolder on each gym 'testimonials' with all the related testimonials like
gyms
-gym A
--testimonials
---testimonial A 1
---testimonial A 2
gym B
--testimonials
---testimonial B 1
---testimonial B 2
<p>Studios: [[*related_studios]]</p>
What does this produce on pages with the TV set:
<p>Studios: [[*related_studios]]</p>
You should see the ID of the page (IDs of pages?) you want to pull in with getResources.

[[!getResources? &parents=`50` &tpl=`testimonials_home` &limit=`5` &sortdir=`DESC` &includeTVs=`1` &processTVs=`1` &includeContent=`1` &depth=`1` &sortby=`menuindex`]]
<div class="client-testimonial-box"> <div class="col-sm-4"> <img src="[[+tv.main_image]]" class="img-responsive"> </div><!-- end col --> <div class="col-sm-7 col-sm-offset-1"> <h2>[[+pagetitle]]</h2> <p class="quote">[[+introtext]]</p> <a href="[[~[[+id]]]]"><span class="button">READ MORE </span></a> <p>Related Studios Test:[[+tv.related_studios]]</p> </div><!-- end col --> </div><!-- end client-testimonial-box -->
Bob asked a question we should have from the start. Let's see what we get. I have a feeling that this ordeal is syntax related. I wonder if you have any errors in your log (Manage -> Reports -> Error Log). Perhaps we're using wrong names in some places.
Million-dollar question: is the getResources tag itself in a chunk?
Another suggestion:
you could try to use Selections from Collections-Extra to pull the related testimonials in
Quote from: Bruno17 at Dec 13, 2015, 01:58 AMAnother suggestion:
you could try to use Selections from Collections-Extra to pull the related testimonials in
Thanks Bruno, let me give that a go and revert.