Is it possible to know which menus are owned by a plugin?

Technically speaking, you can use PHP’s debug_backtrace() function along with appropriate WordPress hooks like wp_nav_menu, add_menu_page etc. to get the file names and function names these WordPress API functions/hooks are called from.

From there, you should be able to determine which plugin is creating or modifying what menu.

However, please note that functions like debug_backtrace() is very resource intensive. So you shouldn’t use them unless it’s absolutely necessary.