WinQueueFromID returns the handle of the queue that was created by the specified thread.

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

HAB    hab;  /*  Anchor-block handle. */
PID    pid;  /*  Process identity. */
TID    tid;  /*  Thread identity. */
HMQ    hmq;  /*  Queue handle. */

hmq = WinQueueFromID(hab, pid, tid);