where is my UDID on my iPhone XS

Get Your iPhone/iPad UDID on macOS without iTunes

Read and follow these steps to find your iPhone/iPad UDID on macOS without using iTunes:

1. Plug your iPhone into your Mac using the USB cable.
2. Click the Apple menu in the upper left corner of your screen > select About this Mac.
3. Click System Report...
4. Expand Hardware and select USB from the list on the left of the System Report window.
5. Select the iPhone from the USB devices listed on the right side of the window.
6. Your UDID is listed as the Serial Number in the details, which you can highlight to copy and paste.

Be sure to add the necessary hyphen after the first eight digits if the device is an iPhone XS or iPhone XS Max.

Source

1. Connect your iPhone to your Mac.
2. Navigate to  -> About This Mac.
3. Click on System Report and select USB.
4. Click on iPhone, and copy the value next to the Serial Number label.

1. Launch iTunes & connect your iPhone, iPad or iPod (device).
2. Under Devices, click on your device.
3. Next click on the 'Serial Number'
4. This should change the Serial Number into the UDID.

how do i get to my UDID

http://www.iphonehacks.com/2018/09/how-find-iphone-xs-max-udid.html

FWIW, the former method no longer works for the iPhone XS and XS Max according to the article BDAqua posted.