How do I locate my iPad in my house or car if it’s not on icloud

Two different questions there.

You can locate a device at iCloud.com/find, you do not need your iPhone

But, if you do not have FindMy enabled, if the device is not powered, and if the device is not connected to a network, FindMy will not work.

If the iPad is in your car or house, the easiest way to find it is to look for it. And it is the only way to find it if you do not have Find My iPad activated.

And in addition to the above correct answers and to explicitly state it, there is no means to remotely enable Find My, whether by serial number or IMEI or otherwise.