As Frank van Puffelen replied, currently there is no realtime information available in Firebase Analytics dashboard. Until this feature is available your next best option is to enable debug logging as defined in the developer documentation:
iOS: https://firebase.google.com/docs/analytics/ios/start#next_steps
Android: https://firebase.google.com/docs/analytics/android/events#view_events_in_the_android_studio_debug_log
When you log event and the event data is uploaded you will see something like this (Android):
I/FA : App measurement is starting up, version: 9080
I/FA : To enable debug logging run: adb shell setprop log.tag.FA VERBOSE
V/FA : Logging event: origin=auto,name=_f,params=Bundle[{_c=1}]
V/FA : Uploading data. app, uncompressed size, data: com.example.app, 348,
V/FA : batch {
V/FA : bundle {
V/FA : protocol_version: 1
V/FA : platform: android
V/FA : gmp_version: 9080
...