SMS notifications on Moto G2 no longer appear
In Settings › Apps, you have to chose the "All" tab: by default, Settings usually shows the "Downloaded" tab, which holds all the apps the user installed. The stock messaging app does not fall into that category, as it comes pre-installed – hence you'll find it on the "All" tab.

Now you've found it, you can take the approach you initially had in mind: calling its context-menu to re-enable notifications by long-tapping the entry here.