It's available in DB2 for zOS v.8 so I assume it's available in other v.8 flavors.
As far as syntax, what are you asking specifically? It's just another column in your table and is used to directly access a row in certain situations.
Code:
CREATE TABLE MYTABLE
(TABLE_ROWID ROWID NOT NULL GENERATED ALWAYS)
SELECT TABLE_ROWID
FROM MYTABLE
etc.etc..