Greetings Etorre,
your query isn't 100% clear - are you referring to Work Clearance Applications or Work Permits?
For the Work Clearance Applications (WCAs) the change documents are saved by default, with no additional customization needed. You will find the changes written as usual to the tables CDHDR and CDPOS, for the Object Class WAPI. The change document are changed for any changes to the header level fields, e.g. Functional Location, Planner Group, dates... but not for Catalog entries or Approvals.
Approval data is logged in the tables WCAGN & WCAGNS.
Status change documents are in table JCDS (see JEST)
If you are referring to Work Permit data, they are handled very similarly. Change documents are enabled by default and Object Class is WAP.
Please feel free to ask any further questions regarding the WCM objects.