I tried 

odoo.define('x_note.note_click', function(require) {
    "use strict";
    var core = require('web.core');
    var Chatter = require('mail.Chatter');
    var MailThread = core.form_widget_registry.get('mail_thread');
    var NewChatter = MailThread.include({
        init: function() {
            this._super.apply(this, arguments);
            var self = this;
            self.trigger('on_open_composer_log_note');
            //on_open_composer_log_note(); tried this and it gives error 
        },
        start: function() {
            this._super.apply(this, arguments);
            var self = this;
            self.trigger('on_open_composer_log_note');
        },
    });
});
But it didn't work. Where is my mistake?