Problem:

The issue here is that the user is getting the error "Toolset plugin cannot connect to toolset"
Solution:
To resolve this. try going to your wordpress backend and click Dashboard -> Updates and then hit Check Again.

Problem:
Add Toolset Hook to my custom plugin

Solution:
The setting for admin bar option is saved within the wp_options table with the key "toolset_options" where we save the settings as serialized array.

You just need to get the value of key "toolset_options" from wp_options table and then unserialize it and look for the array key "show_admin_bar_shortcut" which holds the value either "on" or "off".

If you want to display the "Design with Toolset" menu, you should update the "show_admin_bar_shortcut" to "on" and if you want to disable it then set it value to "off" and accordingly save the "toolset_options" key value.

Relevant Documentation: