Get the values included in a data object [closed]

I'm trying to get some values of a return from a request. Using jQuery, I have the return of the date

$('#protocolo-fk_especie_protocolo').find('option:selected').data()

In this way: $('#protocolo-fk_especie_protocolo').find('option:selected').data('prazo_maximo');

My return is always undefined .

What would be the correct way to access the request date ?