This function returns the desktop-window handle.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HAB     hab;          /*  Anchor-block handle. */
HDC     hdc;          /*  Device-context handle. */
HWND    hwndDeskTop;  /*  Desktop-window handle. */

hwndDeskTop = WinQueryDesktopWindow(hab, hdc);