Passcode what is it and where do I get? Apple one doesn’t work!

It's the passcode you chose when you set up the iPad.

If you forgot your iPad passcode - Apple Support

Are you trying to update the iPad 2 in your equipment profile? If so, that model cannot support any higher iPadOS than v9.3.5/6

The passcode is the one you set up to log onto your iPad.

Thanks