If you set an alert to occur before a Calendar event but aren’t receiving the alert in Notification Center, there are several possible solutions.
Make sure alerts aren’t turned off in Calendar preferences. Choose Calendar > Preferences, click Alerts, then select “Show shared calendar messages in Notification Center” and “Show invitation messages in Notification Center.”
Make sure alerts aren’t turned off in Notifications preferences. Choose Apple menu > System Preferences, then click Notifications. Click Calendar, then select Banners or Alerts as the alert style.
Make sure Do Not Disturb isn’t turned on in Notification preferences. Choose Apple menu > System Preferences, then click Notifications. Click Do Not Disturb, then make sure Do Not Disturb is not set to turn on when you want to receive alerts.
Make sure you set up the alert properly. See Set event alerts and receive notifications.
If the alert is set to send an email, make sure your email address is correct in your card in Contacts. See Edit contact info.