There could be a few reasons behind that:
- Go to the Dashboard > Users > Your Profile > Disable the visual editor when writing and ensure it's unticked.
- Make sure you are on the Visual tab of the editor. If you are using a page builder such as Visual Composer, the text editor will be accessible through a text block.
- Check out the JIG settings > General tab > Advanced > Shortcode editor button minimum user role setting, perhaps it's blocking access to the button.