How do I get the menu under these discussions with the 'flag', 'quote', 'insightful' and 'awesome' buttons etc?
Welcome to the community.
Flagging is a plugin that comes with Vanilla, as is Quotes. These can be enabled from the dashboard.
For reactions, the OS equivalent is the application YAGA.
The original author has not updated it to work with Vanilla 2.6, but another member of the community has. This is a link to the fork: