This answer Find and raise a window in KDE4 with shortcut tells how to set a keyboard shortcut which activates a particular windows. It works wonderfully. But if I close the application and restart it, the shortcut resets. Is there a way to make it persistent?
Go to the following KDE menu
Which allows you to set a trigger and the action
In KDE 5, you need to enable the new action by clicking the checkbox next to it in the tree (or its group, if its group is not enabled).