Tell the slave to restrict replication to updates of tables whose names appear in the comma-separated list. For statement-based replication, only the default database (that is, the one selected by USE) is considered, not any explicitly mentioned tables in the query. For row-based replication, the actual names of table(s) being updated are checked.
"" (an empty string)
Additional information on this topic may be found in the MariaDB Public Knowledge Base.
Information specific to MariaDB SkySQL can be found on the replicate_do_db page in the SkySQL Documentation.