The field path is the hierarchy of the field, which is the path where you can find the field. For the configuration of filters or display pattern, you need to access the value via field id or field path. The field path always starts lowercase.
Example: the field path for a field added to a layer follows its hierarchy, mimicked in the UI, but displayed with names.
1. layer 1.1 field = Product information>Products
2. layer 2.1 field = Descriptive Keyword > Keywords
4. layer 4.3 field = Multimedia information > Sources
You now need the ids for the Layer and field to build the correct path. The UI shows the names.
In the menu "Layers," you find this information per Layer. You can open the Layer directly with the open icon
In F12 developer tools, you can access the JSON information, which lists layerId and fieldId too.
You can open the Display Pattern Editor to see the JSON of a Content Item.