Sonar is a complex program... Its 2.5k pages reference guide is a good source for understanding what is there

You have mixed all together:
* there is no "MIDI Learn ACT mode"
* "MIDI Learn", available in some Software Synth (and some FXes), some ACT plug-ins (also not in all) and in Sonar "Remote control" is MIDI controller related
* "ACT Learn" (the button you can see in the top part of plug-in window) has nothing to do with MIDI (at least not directly)
* automations have nothing to do with MIDI, till they are used on MIDI tracks or controlled by MIDI controller throw ACT plug-ins
* ACT is for controllers only, mouse can not be used as an ACT controller (Joystick, iPad, etc. can, but that is a different topic)
Now to practice, I do not have GB, but all VSTs are equivalent for hosts (including Sonar). Assuming you do not want to use MIDI controller, but want to write an automation:
1) insert GB as a normal FX into the track
2) enable "Automation write" for the track ("W" button in inspector/track view/console) or just for GB ("W" button on top of its interface)
3) start playback, use mouse on the Glitch button.
With some luck you should see the automation lane than
If that works and you want use MIDI: right click on the automation box in the track view, select "Remote control...". Here you can "MIDI Learn"
Finally, from "KVR":
I inquired, "Is MIDI Learn just for the Glitch button or for all knobs/timing settings/etc?"
Their response was, "No, MIDI learn for other knobs beside the Glitch button is not planned atm."
So that means you can somehow "MIDI Learn" it. To use that, click on "VST2" button on top of the window, select "Enable MIDI input". That will put it into Synth rack (it still will be in FX bin!). You can then add MIDI track and set its output to GB (better set "Input echo" to On instead of Automatic on). After that you can use/learn/record MIDI.