The about KDE dialog (which can be called from several places) should show the KDE version numbers in the "about" pane. It used to but now it just says: KDE is a world-wide network of software engineers, artists, writers, translators and facilitators who are committed to Free Software development. This community has created hundreds of Free Software applications as part of the KDE frameworks, workspaces and applications. KDE is a cooperative enterprise in which no single entity controls the efforts or products of KDE to the exclusion of others. Everyone is welcome to join and contribute to KDE, including you. Visit https://www.kde.org/ for more information about the KDE community and the software we produce.
It's in the "About (application)..." -> Libraries tab now.
Note that "KDE" is the name of this community, not any particular product. As such, there are no "KDE version numbers", just like there are no "Microsoft version numbers". There are version numbers for specific products that KDE and Microsoft produce, but not for the organizations themselves. "About KDE" is just that: information about KDE. To find information about the app's own version, go to Settings > "About (application)...". To find the version numbers for Plasma, Qt, the distro, etc use the Info Center app.
It's in the "About (application)..." -> Libraries tab now. While that makes a certain sense it doesn't apply everywhere (eg kmail) and not having the version numbers is a pain. As regards "KDE about" just being a sweet wrapper - that's pretty pointless and a waste of bits those that needs this know this already - the bit we don't know isn't there.