For a web site, I have master and staging, I have worked on staging for about 10 days. How do I tell for sure what has changed since my last merge, or when that merge was? M
Why not simply diff your staging branch against master? That will show you the actual differences in each of your files, and not only those unmerged stuff. Also things you may have dropped when merging from staging to master in the past.
try git diff master..staging
or git diff master...staging to see the diff from their common ancestor to 'staging'.