If your iPhone lacks a home button or your actual home button is not working, you can add a virtual one using AssistiveTouch.
If you want to get the iPad home button on your iPad screen for any reason, you can turn it on via the iPad settings. You may want to add this home button on the iPad screen if you want more options ...
You can use Siri on an iPhone XR, iPhone XS, or iPhone X in two ways: either with the Side button, or through a "Hey Siri" voice command.