Does macOS Sierra support Server Side Copy via SMB and/or AFP? I'm using FreeNAS and it has the option to share data using SMB or AFP. Since I recently learned that AFP is being deprecated, I'm hesitant to use AFP but I'v read that AFP supports Server Side Copy and SMB on Mac does not.

I want to confirm both points with the Ask Different crowd:


Does macOS Sierra connecting to a FreeNAS server via AFP support Server Side Copy?
Does macOS Sierra connecting to a FreeNAS server via SMB support Server Side Copy?


Based on release notes, FreeNAS supports Samba 4.1.4 (SMB3), and thus supports Server-Side Copy when connect with compatible clients.
Unfortunately, the source code of the AFP driver is not free software, so it's difficult to give a definitive answer on that. However, it appears that Netatalk supports copyfile, so it's likely that the answer to that question is yes.
If you look at the source code of the latest version of the macOS smbfs driver, you can see that it does implement the copyfile operation (see smbfs_vnop_copyfile)

According to the release notes, OS X did that since ca. 2013:


  8) Added Server Side Copies (OS X SMB Client &lt;-> OS X/Windows SMB File
  Server)


Whether that actually gets used with FreeNAS, I cannot tell - I have no access to a FreeNAS system.