sys.worker_uuid

Given a logical worker ID, return the UUID of that worker if it was involved in the query where the function is used. If the worker was not involved, the function returns NULL.
sys.worker_uuid(worker_id)

To return a meaningful result, always use this function in a query with a table reference, such as a reference to sys.const.

For example, the first two queries return UUIDs, and the third returns NULL:
premdb=# select sys.worker_uuid(9) from sys.const;
             worker_uuid              
--------------------------------------
 00000000-0000-0000-0000-38b8ebd00393
(1 row)

premdb=# select sys.worker_uuid(3) from sys.const;
             worker_uuid              
--------------------------------------
 00000000-0000-0000-0000-38b8ebd002a3
(1 row)

premdb=# select sys.worker_uuid(16) from sys.const;
 worker_uuid 
-------------
 
(1 row)