Where to find files like pictures and music from Mac hard drive?
If the defaults are in play, then the path to the Users folder of the Macintosh HD when booted from the Recovery HD is:
/Volumes/Macintosh\ HD/Users


Update Note: At the time this was originally posted it was accurate as stated, however, since macOS Catalina the actual physical location is '/Volumes/Macintosh HD - Data/Users'. That said, either path can be used to retrieve user files from.

Within that, the Users directory at the above path, there will be Shared directory and at least one other, which would be your fathers.
It is within that directory you'll find:
Desktop
Documents
Downloads
Movies
Music
Pictures

Etc.

If you are doing this from macOS Recovery, I would probably opt to make a Disk Image of the target Users folder using Disk Utility &gt; File &gt; New &gt; Disk Image from Folder.
Then at least you could do it using a GUI and it would retain all the meta-data too.
Note however, if you have removed the HDD/SSD and have it in an external enclosure connected to another computer, then the path to the Users folder is just /Users, meaning in the root of the volume.