i cant find registration no

If you mean the serial number of the iPad go to Settings>General>About>Serial Number. It is also printed on the back of the device, on the box that the iPad came in and you can see it in iTunes when the iPad is connected to your computer and while iTunes is running - click on the iPad name under devices and then click on the Summary Tab.

If you mean the registration number for your warranty, go back to the link that sent you here.

http://support.apple.com/kb/HT1874?viewlocale=en_US&locale=en_US