Greetings Peter,
As per 's suggestion, have a look at the WCALA table. From this table you can query for 2nd Object Type WD and get the Object numbers for WCAs and WCDs linked.
To get the document numbers, you'll need to join WCALA, WCAAP & WCAHE tables on
WCALA-CHILDART="WD"
WCALA-CHILDOBJ=WCAHE-OBJNR
WCALA-FATHEROBJ=WCAAP-OBJNR
the aim being to select WCAAP-WAPINT for the value of WCAHE-WCNR