Was your old iPad centrally managed by your employer? If so, it may be managed by an MDM platform that could inhibit use for other purposes.
If the iPad is your own, purchased by yourself, you should be able to recover use of the iPad. Whilst the AppleID may be the email address of your employer, the email address is simply used to identify the AppleID account (as the username). You will need to initially concentrate your effort on recovering access to the AppleID account - as, until you do so, you’re likely to encounter multiple issues that will thwart your attempts to reuse the iPad.
The AppleID and associated password, if forgotten, can be recovered here:
https://iforgot.apple.com
To recover your credentials, you’ll need access to any one of the following - to which you can receive account reset:
- 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
Assuming the AppleID account was your own (i.e., not managed by your employer), unless your AppleID account has not been fully/correctly configured or has been seriously neglected, recovery of the AppleID and password should not be overly difficult.
More information about recovery of your AppleID:
If you forgot your Apple ID - Apple Support
More information about recovery of your AppleID password:
If you forgot your Apple ID password - Apple Support
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
When you have recovered the AppleID credentials, you can consider necessary steps to reuse the iPad.
If you intend to reuse the iPad with a different AppleID, you would be well advised to prepare it properly for reuse - as this will ensure that the Activation Lock associated with the original AppleID is removed, along with all data and other sensitive information:
What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support