In this example I'll show you how you can show a Toast by touching an AutoNotification notification.
You can, of course, do whatever you want, instead of showing the toast

STEP 1 - CREATE PROFILE THAT DOES WHAT YOU WANT

• Create a new profile in Tasker
• Use the AutoNotification event condition

You could also use the AutoApps condition if you wanted. That condition will receive commands from any AutoApp which is handy if you want to send the same command from different apps.

• Set the Message Filter to do something

The message filter can be anything you want. In this case, since it's a generic example, I simply used do something but you can use whatever command you want. More info on the AutoApps command system here.

• Enble Exact Message so that only this exact command will trigger this event

If you didn't use the Exact Message option, then a command like do something now would also trigger this event. You may want that, but for this example I want it to react to just do something

• Accept these settings and create the profile's entry task

STEP 2 - SHOW TOAST

• Add a Flash action
• Set the text to I'm doing something

This will show up whenever AutoNotification receives the do something command

STEP 3 - CREATE NOTIFICATION

• Create a new task called Create Notification
• Add an AutoNotification action
• Set the Title and Text fields to anything you want
• Set the Action field to exactly do something

It's very important that this action matches the message filter set in the profile event configuration, or else the event won't trigger. Make sure there aren't any extra spaces somewhere in the action

• Go back to Tasker and run the Task
• Make sure that the notification shows up
• Exit Tasker so everything is saved.

STEP 4 - TEST

• Open the notification tray
• Touch the AutoNotification notification
• You should see the toast show up at the bottom

If you want to get creative you can then use the AutoApps Command System to send more complex commands. Check out an example here.