menu-bar-menu-at-x-y

menu-bar-menu-at-x-y is a built-in function in `C source code'.

(menu-bar-menu-at-x-y X Y &optional FRAME)

Return the menu-bar menu on FRAME at pixel coordinates X, Y.
X and Y are frame-relative pixel coordinates, assumed to define
a location within the menu bar.
If FRAME is nil or omitted, it defaults to the selected frame.

Value is the symbol of the menu at X/Y, or nil if the specified
coordinates are not within the FRAME's menu bar. The symbol can
be used to look up the menu like this:

(lookup-key MAP [menu-bar SYMBOL])

where MAP is either the current global map or the current local map,
since menu-bar items come from both.

This function can return non-nil only on a text-terminal frame
or on an X frame that doesn't use any GUI toolkit. Otherwise,
Emacs does not manage the menu bar and cannot convert coordinates
into menu items.