Look Me Up By Email problem
The GUI is located in the Apple ID > iCloud >  Options -> Look Me Up By Email window.

Mine is blank:



So why is mine blank and your filled? Because Apps that use iCloud can offer this service to other iCloud users so that they can find you.

As discussed here and here and here and here, one way to remove the app is to delete it.  It may be that some apps give you the ability to turn it on or off, but it's really an app thing.

EDIT:

If the MarginNote application is not installed and you are still seeing this GUI, try this:


Open Terminal.
Type: find $HOME -name '*MarginNote*' -ls
Post the output.


If that doesn't work, then try this: 


Install on a new machine (or in a VM), just so we know everything is clean.
Log in but do not add your Apple ID.  You should not see anything in the "look me up by email" GUI.
Log into iCloud but disable every service. If you see things in the GUI, then it's somewhere in your iCloud count that you can't reach.
Sync just the iCloud drive. If it appears, then there is a file in your iCloud drive that has this information. Go into Terminal and list all of the files with the "find $HOME -name 'MarginNote'