This function returns a window handle to various windows created as a part of a secondary window.

#define INCL_SECONDARYWINDOW
#include <os2.h>

HWND     hwnd;    /*  Secondary window handle. */
ULONG    ulFlag;  /*  Flags. */
HWND     hwnd;    /*  Reqested window handle. */

hwnd = WinQuerySecondaryHWND(hwnd, ulFlag);