Get value of a field from a foreigKey in Django Models
This should work:
try:
    testo_sequenza = Test.objects.get(pk=idObj)
except Test.DoesNotExist:
    # do here what you need the program to do if not found. maybe a return if function or a continue/break if you're in a loop
    print("Testo Sequenza not found")
sequenza_test = testo_sequenza.sequenzaTest
serie_di_movimenti = sequenza_test.serieDiMovimenti

Also you should check
serieDiMovimenti = models.TextField(blank=False, null=False, default="")

Because if you want it to be "optional field" then it would be blank=True

I have two classes in my Database in Django
class Test(models.Model):
    sequenzaTest = models.ForeignKey("SequenzaMovimento", null=True, on_delete=models.SET_NULL)

class SequenzaMovimento(models.Model):
    nomeSequenza = models.CharField(max_length=50, blank=False, null=False)
    serieDiMovimenti = models.TextField(blank=False, null=False, default="")

Now, every Test object created can be associated with just one SequenzaMovimento object. Different Test objects can have the same SequenzaMovimento
Now, I know the primary key of my Test. How do I find the serieDiMovimenti inside the SequenzaMovimento object which is linked to the Test object?
I can get the sequenzaTest from the Test object with
testo_sequenza = Test.objects.get(pk=idObj)
testo_sequenza.sequenzaTest

but I can't find to understand how access serieDiMovimenti
