Those are defined in two places. Check your custom UI folder for eq2ui_proxyactor.xml and if you see it, delete it. Reload the UI and see if the feathers reappear. if they do not, then check the \images folder of your custom UI for a file called widgets02.dds. Delete if found. With both of those files gone, that will take you back to the defaults for quest feathers on mobs.
Also there is a setting in Options > User interface > Name and Chat Bubble, I believe it's "NPC Quest Target Icons" that you can check. IIRC that controls whether or not the round icons in your screenshot appear.
If none of that helps, try loading the entire default UI and check the status of mob feathers.