How to disable Adobe Core Sync app on OS X from being launched automatically?

You can disable this Finder Sync extension from the System Preferences → Extensions pane (grey puzzle piece icon) – just untick Finder under the app name in question.

Then log out and back in (or restart if you have more than one user logged in to your Mac)

In OS X, the Finder Sync extension point lets you cleanly and safely modify the Finder’s user interface to express file synchronization status and control. Unlike most extension points, Finder Sync does not add features to a host app. Instead, it lets you modify the behavior of the Finder itself.

Extensions are parts of an app that are able to integrate with certain core components of the OS. Finder Sync extensions in particular enable tighter integration with Finder by way of sync status badges, and allowing buttons to be added to the toolbar, sidebar, and right click menus.

OS X keeps a database of all known apps on your computer, and this also includes any extensions (.appex bundles). When Finder launches, it queries this database for Finder Sync extensions and launches them. For security reasons, each extension lives in its own process.

launchctl has changed for the better in 10.11.4

Type the command without arguments to get the help. You'll see new domains to search and new commands.

• Printing the system root

  launchctl print system
  

• Printing details about a particular service within the root domain

  launchctl print system/<com.example.service>
  

For your processes: if it's not in the system domain it's probably in the domain of that particular user.

• Checking the domain of a particular user

  launchctl print user/<uid>/
  launchctl print user/<uid>/<com.example.useragent>
  

However, since you'll be logged into the GUI, you might want to check the domain of the GUI, which is kept separate.

• Checking the domain of the GUI

  launchctl print gui/<uid>
  launchctl print gui/<uid>/<com.example.service>
  

• GUI domains are for processes that apply to a user interface.

• User domains are for processes that invoke daemons that only apply to a particular logged-in user.

• System domains are for system daemon processes, and apply to all users within that system.

To learn more, read man launchctl or read Apple's article about Creating Launch Daemons and Agents

Another guess would be to check in /Library/StartupItems.

But launchctl does not require your service.plist to be located in one of those directories.
In fact, you do not even need to have a file (as seen in the launchctl submit).
So as long as you register it with launchctl load|submit, it will be kept running/starting.

I think your best way is to disable the tool with launchctl directly or by using an Application like LaunchControl.

The problem is that over the last years Apple has introduced other ways to auto-start items than having plists in specific folders like it works with launch agents and daemons. xpc services, smloginitems are not located in these places but are registered in the launchctl database (can be seen by launchctl list) but this specific adobe plugin obviously gets loaded at start but is NOT listed by launchctl at all. you can see some info by using launchchtl print user/501 but not by launchctl list. so what exactly is ACCFinderSync and why does it not show up? the hole launch system is kind of splintered up atm and it is very complicated to observe all forms of startup items. the big question here is: what are application extensions (appex) and how can they get detected (and disabled) at command line level if not by launchctl.