I have a Sharepoint Farm with some servers.
Our DBA is going to do a planned SQL maintenance and the server that exclusively hosts SQL Server requires to be offline.
What I, as Sharepoint Administrator, need to do before and after this down time?
I agree with Trevor that you don't have to do anything however, generally if the SQL servers are going to be offline, it's a good idea to shut the SharePoint servers down before SQL goes offline and start them back up after SQL is back online again. This provides a good opportunity to clear any cobwebs from memory while shutting all of SharePoint down gracefully.
If you choose to leave your SharePoint servers running, I would run a check on all SharePoint service apps after the SQL maintenance is done. Service apps will not gracefully stop but instead throw continual errors. If you have environmental monitoring such as SCOM, you'll want to mute alerts for the SharePoint servers or your inbox will be flooded. Lastly, when the databases are up, if something isn't working, like search, you can restart the service app to fix it.