$.ajax({
    url: '<?= base_url('login/Pesquisar'); ?>',
    type: 'POST',
    data: $("#formulario_pesquisa").serialize(),
    dataType: 'json',
    success: function(data){
        alert(JSON.stringify(data))
        alert(Object.keys(data));
        alert(data.email);
    }
});

alert(JSON.stringify(data)) >>> {"cnpj ":"68.207.717/0001-42","email ":"teste.teste@email.com","Logado":true)

alert(Object.keys(data)); >> cnpj ,email ,Logado

alert(data.email); >> undefined

var json = {"email ":"teste.teste@email.com"};
console.log(json.email) <= undefined

var json = {"email":"teste.teste@email.com"};
console.log(json.email) <= teste.teste@email.com