Originally Posted by bigrigdriver
The key sequence may already exist. Try ctrl-tab and alt-tab.
No, I am talking about window tabs, not tabs within windows (like tabs in Firefox).
I answered my own question. Go to the "Global Keyboard Shortcuts" system setting, select the KWin "KDE Component", search for "tab", and "Walk Through Window Tabs" will appear. You can then set a keybinding for it.