I do not know the latest but If you see Oracle and DB2 certifications syllabus you can have a better opinion. For me, some topics are (by using VirtualBox) you can speak about
- Oracle RAC
- Oracle stands by
- Disaster Sites
- Backup & Restore
- Partial Backup & Restore
- Migrations of DB
- Extraction of Data
- a very good theme is DB Tuning
- and many more
If you need advice the (for Oracle)
Oracle DBA and development articles, scripts, HOWTOs and forums (8i, 9i, 10g, 11g, 12c, 13c, 18c, 19c, 21c)
Oracle DBA and development articles, scripts, HOWTOs and forums (8i, 9i, 10g, 11g, 12c, 13c, 18c, 19c, 21c).