After nearly 10 years of working with CMOD, I've finally made the Certification at the beginning of this year (would be a shame to be a CMOD specialist at IBM without Certification, isn't it!!)
So if you understand the official manuals, know ODWEK (not at the deep API level!), know the relationship from CMOD and other IBM products (CM/FileNet/TSM/...).
Know a bit about the Indexer (ACIF, PDF, ...)
How the admin works (cache, migration, Cabinets, Holds, Printer, ...etc...)
the CMOD configuration (ars.ini, ars.cfg, ...)
Well everything in the manual. If you know it, or at least do a refresh...
I think that since you have already knowledge and experience from CMOD, then by reading the whole set of manual for a refresh, you'll have nothing to fear.
Good luck!
Alessandro