This function returns the focus window. It is NULLHANDLE if there is no focus window.

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

HWND    hwndDeskTop;  /*  Desktop-window handle. */
HWND    hwndFocus;    /*  Focus-handle. */

hwndFocus = WinQueryFocus(hwndDeskTop);