For me your code looks like very pretty.

Sometimes I write in this manner

    Dnianas.Notification = {
        elements: {
            opennotifiiSel: '#opennotifii', //also rename selectors to camelCase, for example
            boxsendnotifSel: '#boxsendnotif',
            boxnotificationsusersSel: '.boxnotificationsusers'
        },
    
        constants: {
            NOTIFICATION_FADE_OUT: 200
        },
    
        URL: {
            markAsRead: '/notifications/read',
        },
    
        init: function() {
            this.bindEvents();
        },
    
        bindEvents: function() {
            $(document).on('click', this.elements.opennotifiiSel, this.markAsRead.bind(this));
        },
    
        countNotifications: function() {
            var ids = [];
    
            // Add unread notifications to the ids array.
            $(this.elements.boxnotificationsusersSel)
                .children() //why we use children() before find()?
                .find(this.elements.boxsendnotifSel)
                .each(function collectboxsendnotifIds() {
                    if ($(this).data('read') === 0) {
                        ids.push($(this).data('id'));
                    }
                });
            return ids;
        },
    
        markAsRead: function() {
            var self = this;
            var ids = this.countNotifications();
    
            if (ids.length > 0) {
                $.ajax({
                    url: self.URL.markAsRead,
                    data: {
                        notifications: ids,
                        _token: token,
                    }
                }).then(function(data) {
                    self.renderNotificationCount(data);
                });
            }
        },
    
        renderNotificationCount: function(data) {
            if (data.seen) {
                $(this.elements.opennotifiiSel + ' .not_nu1').fadeOut(this.constants.NOTIFICATION_FADE_OUT);
            }
        }
    };