If your forget your device Passcode, or if your iPad is disabled, all locally stored data is lost. All data stored on the device is encrypted “at rest” - and the encryption key is stored within the iPad security chip (the Secure Enclave); your device Passcode is the key to the lock - that releases the encryption key.
Once your iPad is disabled, nothing and nobody can access the encryption key that protects the data on your device. Without a Passcode, the only way to recover access to the device is to follow the restore process - which completely wipes the device. This is why keeping a backup of your device data is so important.
If your iPad is disabled, or you have forgotten your iPad passcode, you’ll need to follow this process - at the end of which you can restore your data from your iCloud or iTunes backup:
https://support.apple.com/en-gb/HT211078
You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).
You’ll also need your AppleID and associated password. If these have also been forgotten, they can be recovered here:
https://iforgot.apple.com
To recover your credentials, you’ll need access to one of the following:
- Your primary email address mailbox that corresponds with your AppleID
- Any of the secondary/recovery email addresses that should be configured for your AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID
Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.
More information about recovery of your AppleID:
https://support.apple.com/en-us/HT201354
More information about recovery of your AppleID password:
https://support.apple.com/en-us/HT201487
When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:
https://appleid.apple.com