Look in Settings
Go to Settings > General > About. To the right of the Model Number, you'll see the part number. Please be aware that's not the model number. To see the model number, you must tap the part number displayed to the right of the Model 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.