Look in Settings
Go to Settings > General > About. To the right of Model, you'll see the part number. To see the model number, tap the part number.
Look on your device
On an iPhone 8 or later, to find the model number, remove the SIM tray and look in the SIM tray slot. Make sure that you're in a place with bright light overhead. The model number is on the upper side — the side with the display.
On an iPhone 7 or earlier, an iPad or an iPod touch, find the model number on the back of your device.