So A, B, C, D, and E are not Nodes? And the dashed lines from “Activity Two” to those items are not Links? Hmmm, that would be so easy to implement if they actually were Nodes and Links…
I assume you don’t have any problem defining the “Activity” nodes, and the “trash can” button in the Adornment. However it still isn’t clear to me whether that is a “Selection” Adornment or if it is just an Adornment that you programmatically show and hide based on mouse events. Either way can work, but they really are different. If the user executes the SelectAll command (Ctrl-A), do you expect all “Activity” nodes to get those Adornments? Or is there at most one Adornment visible at a time? Or some other behavior?
For selection adornments, please read GoJS Selection -- Northwoods Software and see this sample: Grafcet Diagrams.
For hover adornments, please see this sample: Buttons that show on Hover.
Although in both cases you might not want to use a button-like object – that interaction requirement isn’t clear to me from your description.