I bought secondhand iPad years ago , it’s locked I forgot my Apple ID and what should I do ??

To clear an Activation Lock, you will need the password of the associated Apple ID, or the original purchase receipt and matching photo ID and a discussion with Apple Support.

To (try to) recover the Apple ID and password:

If you forgot your Apple ID password - Apple Support

If you forgot your Apple ID - Apple Support

How to use account recovery when you can’t reset your Apple ID password - Apple Support

How to request access to a deceased family member's Apple accounts - Apple Support

Contact Apple for help with Apple ID account security - Apple Support

The displayed Apple ID info in the prompt contains a hint about the associated email address.

Activation Lock is a theft deterrent mechanism. A theft deterrent that is easy to bypass would not be much of a deterrent. No, nobody here in the Apple discussion forums can help you clear Activation Lock. Only the person holding the Apple ID and password, or Apple, can clear this lock. For Apple to clear the lock, you will have to provide a receipt with proof of original purchase and with matching serial number, and provide matching personal identification, or similar materials.

Would this be your iPad Passcode, or your AppleID and associated Password?

Is the iPad disabled, or Activation Locked?

Activation Lock

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.

If you have the necessary documentation, Apple have recently introduced a new portal though which you may be able to request release of an Activation Lock:

How to remove Activation Lock - Apple Support & start an Activation Lock support request.

Disabled

If your iPad is disabled, or you have forgotten your iPad passcode, you’ll need to follow this process:

If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support

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).

AppleID

You’ll need the AppleID and associated password. For which you’ll need the owner to assist. If these credentials have also been forgotten, they can be recovered by the owner 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:

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