I have ipad wifi only but it is iCloud lock but I have purchase in second hand n I want to open my iPad lock ...I have that owners birthday and name n address n serial number

Having their information is not going to help you. You are going to need them to remove the device from their iCloud account. See this information and share it with them to allow them to unlock the device. What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

If you cannot get them to do this, then you will not be able to activate the device.

Hi

Only the owner who knows the apple ID that ipad is locked to can remove lock.

If you can contact them ask the to go to find my iPad on an apple device they have and remove that ipad from the list .

If they cannot do this you can never use iPad Get your money back it may be lost / stolen .

Cheers

Brian