The default plugins are all in plugins\Default\ , the coe plugin is plugins\Default\BuffLists\ConventionOfElementsBuffListPlugin.cs (this one shows the rotation next to the portrait)
To see the icon that you have marked, you must add to plugins\User\PluginEnablerOrDisablerPlugin.cs this code:
Code:
Hud.RunOnPlugin<PlayerBottomBuffListPlugin>(plugin => {
plugin.BuffPainter.ShowTimeLeftNumbers = true;
plugin.RuleCalculator.Rules.Add(new BuffRule(430674) { IconIndex = null, MinimumIconCount = 1, ShowTimeLeft = true }); // ConventionOfElements
} );