When the pane with the window previews (when windows are grouped) is shown it would be helpful if the window title would additionally be shown. That would help to identify the correct window.
The popup emerges from the task manager entry, which has the title in it anyway, no? Do you have multiple rows in task manager?
Created attachment 100941 [details] task manager Yes, it has a title but it is generic: e.g. "dolphin" but each dolphin window has a different title (see also related wish https://bugs.kde.org/show_bug.cgi?id=229810) Yes, I have two rows.
By pane do you mean the tooltip ...?
Yes, the tooltip with the window previews in it.
This was done in the 5.9 tooltip redesign.