Now, JMES Path Query supports also non-data source placeholders like insights, filterParams, inputFields. Find more general information in JMESPath documentation.
You can configure your JMES Path Query from the Data Transformation pane. When editing a widget, you can view all available placeholders in the Test Parameters tab. See the example below::
For more information about Data Transformation, refer to the respective Data Transformation section in each widget where available.