You can easily see which dom0 updates you have received in the past with this command (in dom0):
dnf history
This will give you a numbered list of events, including the date and time of each event. By default, the most recent event is at the top. You can then view the details of any event with this command:
dnf history info <ID_NUMBER>
For example, if you wanted to view the details of event 25, the command would be:
dnf history info 25
This will show you a detailed view of that event, including a list of all packages altered, their version numbers, and even scriptlet output.
(Note: This is not a Qubes OS feature. It’s a DNF feature. Since dom0 is based on Fedora, we have inherited this feature.)