Did you try using the Help menu within Virtuoso and then searching the documentation for the function name?
If using IC61X you have cdnshelp which you can invoke from the command line, and you can search in that. Or if using IC5141 you can run cdsdoc. Or you can search on Cadence Online Support. If you have multiple streams in your path, you might want to make sure you explicitly run <ICinstDir>/tools/bin/cdnshelp (or cdsdoc) to ensure you pick up the right docs.
Or if that's too tough (it really shouldn't be), the docs are in <ICinstDir>/doc . This function (and other database functions) are in <ICinstDir>/doc/skdfref/skdfref.pdf . You might also want to have a good read of the SKILL Language User Guide which is in <ICinstDir>/doc/sklanguser/sklanguser.pdf .