Hi Anil.sardana,
Welcome to Apple Support Communities! We appreciate you reaching out for help getting files from your app to save in iCloud. We're glad to point you in the right direction.
To ensure we understand correctly, it sounds like Notability isn't showing that any storage is saved in iCloud when checking the storage amount in Settings > [your name] > iCloud > Manage Storage > Notability. Is this correct?
Are other installed apps able to store and sync data using iCloud without issue? If the issue is isolated to Notability, we may refer you to the developer directly to inquire further.
First, we can recommend restarting your device. If you have another device you use with iCloud, such as an iPad or Mac, you may want to check Notability on one of those devices to see if your data syncs through iCloud to those devices.
Otherwise, we can recommend deleting the Notability app as a last resort, in order to reinstall it and test again. It's important to note that deleting the app will also delete your data in the app.
If you're able to further isolate the issue to Notability, you'll want to contact the developer directly to inquire further. Here's a guide with the steps to contact the developer:
How to contact an app developer - Apple Support
Have a great day!