driver.findElement(By.cssSelector("i [class='glyphicon glyphicon-chevron-down']")).click();

<div ng-class="{acknowledgedgradient: (item.acknowledgementRequired && !item.isAcknowledged)}" class="ng-binding ng-scope acknowledgedgradient"> Announcement 3 <span class="pull-right"> <i class="glyphicon" ng-class="{'glyphicon-thumbs-up':item.acknowledgementRequired && item.isAcknowledged}"></i> <span class="acknowledged-whitespace"></span>