Unfortunately, there are only three ways that I'm aware of to edit notification settings.
During the creation of the proof: If you used the "New" dropdown under documents, you can change notifications settings from the right side as indicated in a screenshot from a previous comment.
During the creation of the proof: If you clicked "Generate Proof" from an existing file, it will use the default user settings. You have to change the default settings on EACH user. There is no global setting.
After creation of the proof via the proof details link on the details tab as someone else mentioned.
To disable notifications completely, we change the following settings at the User level, and we have project coordinators double-checking these settings are set from the Proof Details tab before sending links to clients. Under "Default Proof Settings", we activate subscriptions so folks outside of Workfront can share links. But we turn off the emails. We also set "Reviewer" as the default role. Under "Default Email Alert Settings", we disable emails in pretty much every case. The lack of a global setting makes it very painful to set up new options across the board. We have dozens of users creating proofs and need to deactivate all notifications except to the owner, as we don't want reviewers getting notifications with every comment. I've submitted an Idea to Idea exchange to give us "global" settings that we can set along with the user and per proof settings, if anyone would like to up-vote it: "https://support.workfront.com/hc/en-us/community/posts/360002738914-Global-Settings-for-Proofs-including-Subscriptions-Roles-etc-">
https://support.workfront.com/hc/en-us/community/posts/360002738914-Global-Settings-for-Proofs-inclu... Alex Mueller Thomson Reuters - Tax and Accounting