The Debian packaging of volume-el is maintained in git, using the merging workflow described in dgit-maint-merge(7). There isn't a patch queue that can be represented as a quilt series.
A detailed breakdown of the changes is available from their canonical representation - git commits in the packaging repository. For example, to see the changes made by the Debian maintainer in the first upload of upstream version 1.2.3, you could use:
