Reminders not showing up in notifications center

Have a look at this article: macOS Sierra: Use Notification Center

In Notification Center, click Today, then do any of the following:

• Get details: Click an item in a widget. For example, click an item in the Weather widget to show the hourly and five-day forecasts. Or click an item in the Calendar widget to open the item in the Calendar app.

• Take action: Click a widget item or its checkbox. For example, click an icon in the Social widget to post your latest news to LinkedIn, Facebook, Twitter, or Messages. Or click a reminder’s checkbox to complete it.

• Customize a widget: Move the pointer over the widget, then click the Info button that appears.

• Reorder widgets: Click Edit at the bottom of Today view, then drag a widget up or down.

• Add or remove widgets: Click Edit at the bottom of Today view. To add a widget, click the Add button .To remove a widget, click the Remove button ; the widget is moved to the list of available widgets.

• Get more widgets: Click Edit at the bottom of Today view, click App Store, then buy or download widgets from the App store. For more information about buying and downloading apps, see Find, buy, and download apps.

If you don’t see an expected account in the Social widget, choose Apple menu > System Preferences, click Extensions, click Share Menu, then select the account. Only accounts that allow posting or messaging appear in Today view.