I'm relatively new to KDE development and stuck with doing this. I'm trying to fix a bug for Akregator where the users can not use Ctrl + C to copy the selected text. Looking into the source code, I see that Akregator uses BrowserExtension to display websites though there's no code which enables the copy action.
If someone can do this, please help me and also explain your code a little bit because I'm also not a really good developer myself.

BrowserExtension likely provides the Copy action itself. I suggest you continue to look in kdelibs for this code, which I believe is also used by Konqueror to perform web browsing.

I've had a look into the Konqueror code. I think Konqueror doesn't use BrowserExtension for the html view, but rather uses it for other thing.
There's a strange thing which we really need to consider: Pressing Ctrl + C does do something. Specifically, it clears the clipboard but doesn't add the selected text to it. Though I do not know how to debug this (with gdb).

I would recommend asking about this on the kde-devel@kde.org mailing list, as it is outside my field of expertise. I suspect you may have stumbled upon a bug in Konqueror.