Hey there! I can certainly understand wanting your alarm to show on your screen! You may have Sleep as Android enabled under Edge Lighting (Edge Lighting on some versions). This causes the alarm popup not to appear above the lock screen because the notification appears as a light around the edge of the screen. Disable Border lights for Sleep as Android in your device's settings.
You may also want to double-check the time and make sure that the alarm is turned on. If that doesn't work, try clearing the cache and data of the Clock app. To do this, go to “Settings,” then “Apps,” then “Clock.” From here, you can clear the cache and data.
