On the Planner within the Items properties there is a checkbox labeled "ShowDeleteButton".
Wnen true the small red button with an X appears at the right of the displayed item.
There is nothing in the Items.Events that reflects anything to do for this button nor is there anythnig in the Planners Develpers Guide that explains this button.
How do I access the event when this button is clicked?
We have seen this inconsistency between TPlanner & TPlannerMonthView and have now fixed this. The next update will have the OnItemDelete event exposed that will be triggered when the delete button is clicked and will allow you to intercept this.