I would like to display multiple clocks on my Nexus 5X running Android 7. I selected multiple cities like explanied here but it doesn't really work.
It should look like this:
Unfortunately, Google removed the option to add custom widgets to the lockscreen in Android 5.0 and didn't bring it back, for whatever reason.
The only option you have is rooting your device and installing xposed framework. There is a module called 'Lock Screen Widgets' which allows you to add custom widgets to the lockscreen (hence the name). Then, just add a clock widget with multiple time zones (if the stock clock doesn't support that, you might need to download a different one from Google Play Store)
Good luck :D