Neither way works in Wayland. A program can know where it was clicked but not where the pointer was immediately before that. For that matter Wayland doesn't have a concept of "the" pointer; there may be multiple pointers.
> Using the wl_seat.get_pointer request, clients may obtain a wl_pointer object. The server will send events to it whenever the user moves their pointer, presses mouse buttons, uses the scroll wheel, etc — whenever the pointer is over one of your surfaces. [...] The server sends this event when the pointer moves over one of our surfaces, and specifies both the surface that was "entered", as well as the surface-local coordinates (from the top-left corner) that the pointer is positioned over.
So the program should know the pointer's local coordinates.