How do I get spells with periodic effects to show in the group/target windows?

[Darqwood]

If I understand your question, this is three separate issues.

To put a heal over time spell icon on the Group window you can use the Window Manager to replace one of the five reference-cast icons. Click the blue button in the upper left-hand corner of the Group window and choose a different spell from the dropdown. If you don't see the spell you want, you can edit the settings manually or use the DarqUI utility to change it.

Whether or not a heal over time buff icon appears in the Target window is controlled by the game. If your heal spell doesn't apply a buff icon to your target (ally) there is no way for us to add one.

If your heal spell puts a buff icon into your Maintained Spells window, you can track it using the Maintained Spell Monitor. There is plenty of info about that in the Help window in-game. Open /help and click the DarqUI Help tab.