Change the name of "Panel" written on Panel page? I want to change it to "Your Groups"
You can modify GJs frontend from its template files found below.
components/com_comprofiler/plugin/user/plug_cbgroupjive/templates/default/
It's best to copy the default folder and rename it (e.g. default_new). Delete all the files you don't intend on modifying. Then select your new template from GJ configuration. Next modify your files as needed. Any missing files will auto inherit from the default template. This basically allows you to do template overrides.
Is it possible to have a menu just with the joined group of the User?
What menu items are available you can generate within GJ > Menus.