Starting with iOS 12, you can receive notifications without showing up on the Lock Screen, displaying banners, or playing sounds. In the Quiet Notifications mode, a notification only appears inside the Notification Center. While this feature is excellent when you want information to arrive without any prompts, you can disable it whenever the need arises.
Step#1: From the Notification Center, pick the notification you want that should be displayed on the Lock Screen, appear as a banner, and play a sound.
Step#2: Slowly slide the notification to the left till you see the Manage button. Tap it.
Step#3: Tap Deliver Prominently to disable quiet notifications.
Step#4: The notification will now appear on the Lock Screen, display as a banner, and play sound.
Alternatively, you can use this method.
Step#1: From the Settings, tap Notifications
Step#2: Select an app.
Step#3: Under Alerts, tap Lock Screen, Banners, and Sounds for notifications to be delivered prominently.