How to load fields by target type?
By what you can see in this var dump the field can hold any paragraph type, so you don't know which fields it may contain.

When you have restricted the field to one paragraph type, then load the field defintions for this type: 

$fields_paragraph = \Drupal::service('entity_field.manager')
  -&gt;getFieldDefinitions('paragraph', 'my_paragraph_type');