get_field_object( 'domaine_de_formation' )
returns the field settings for the field. choices you added when creating the field will be in ['choices']
.
If you are trying to get the values that are set when adding/editing a post then you should use get_field()
not get_field_object()
or you need to look in ['value']
of the array returned by ‘get_field_object()`.