Template override question

Hi, i have a category in place, one file in the root category-testing.php and another in the loop-templates. This all displays my posts ok, in columns etc.

The problem im having, is when i click the ‘read more’ and it opens the post, and its this template i cannot find, i need to know which template file it is loading after i hace clicked ‘read-more’.

At present, when i click ‘read-more’ it’s displaying my post on a full width page, and i want to override this, so when a user clicks on a post, it will display the post in a much narrower column.

I just need to know the template file to alter, if anyone knows

the pages, i have overrided at present are
/catagory-testing.php (my category slug is testing)
/loop-templates/content-testing.php
/page-templates/testing.php (not sure i need this, but created one anyway)

I have a few posts in a category, with the slug set at testing

Cheers

Rob