How can I determine which module is associated with a field plugin?
The answer to the question title should be straightforward. You can get the extension from plugins via getProvider(). So you could make a list of all FieldType plugins or get the provider of a specific field type directly from the plugin defintitions:

$module = \Drupal::service('plugin.manager.field.field_type')
  -&gt;getDefinition($field_type)['provider'];


For field definitions this is a bit more complicated. Field storages have this method as well, but for configured fields it always returns the module field. This is not what you want. But there is a different place. When creating field storages the provider of the field type plugin is stored in the property module. So starting from FieldDefinitionInterface you should be able to get the module name:

$module = $field_definition-&gt;getFieldStorageDefinition()-&gt;get('module');