ui:menuTriggerPress

Indicates that a menu trigger is clicked.
For example, the ui:menuTrigger component registers this event so it can be fired by the component.
<aura:registerEvent name="menuTriggerPress"  type="ui:menuTriggerPress"
                    description="The event fired when the trigger is clicked." />
You can handle this event in a component that extends ui:menuTrigger, such as in a ui:menuTriggerLink component instance.
<ui:menu>
    <ui:menuTriggerLink aura:id="trigger" label="Contacts" menuTriggerPress="{!c.triggered}"/>
        <ui:menuList class="actionMenu" aura:id="actionMenu">
            <ui:actionMenuItem aura:id="item1" label="All Contacts" click="{!c.doSomething}"/>
            <ui:actionMenuItem aura:id="item2" label="All Primary" click="{!c.doSomething}"/>
        </ui:menuList>
</ui:menu>
This client-side controller retrieves the label of the trigger when it’s clicked.
({
    triggered : function(component, event, helper) {
        var trigger = component.find("trigger");
        
        // Get the label on the trigger
        var triggerLabel = trigger.get("v.label");
    }
})