Since installing Logos 8, I no longer get notifications for the logs of what's new or fixed in updates.
Where does one now go for the changelog?
Release notes normally accompany the release announcements. If you are talking about the link to release notes you could access from Logos (L7) that is not currently available in L8.
You can currently either check the wiki or the appropriate forum announcement thread (which contains a link to the release notes).
Faithlife plans to bring back the home page notification in the near future.
You can also access the Logos Wiki from the help menu in Logos. From there you would scroll down and click "Logos 8 Release Notes."
