Which log file(s) should I be looking at to diagnose CORL problems (also, specific problem with Organizations - Contacts)

[KerryBouchard]

I am new to supporting a CORAL installation at our library. My main question is what log files or other diagnostic tools should I be using to diagnose problems. The php-fpm error.log is not showing me anything that appears to relate to the problem below.

The problem I'm working on right now is that in Organizations, when we click the "Contacts" link for any organization, we just get two spinning icons and nothing ever loads. Date in the ORG_Contact table in MySQL appears to be fine.

Thanks, Kerry