How do I know if an update requires restart in macOS Sierra?
When you look at the Updates list in the Mac App Store, it will indicate in the info if a restart is required. Below is an example of this:



You will see the words Restart Required followed by an icon of a white triangle within a grey circle (looks like a reverse play button).

Prior to installing the update, just check the info against each update to see whether any of them require a restart.

Security updates and OS updates usually require a restart. Most other apps don't.