How do I perform the filling of an information that is in a JSON complex type?

Do as Maycon quoted, your object must have the same name with the same property with identical names that will work.

The name of the properties of your json can be equal to the object you are receiving as already quoted (I think this is particularly horrible, rs). I'll show you a more "elegant" way of solving, using Newtonsoft.Json .

First instantiate it in your project:

using Newtonsoft.Json;

Then on your object

public class RootObject
{
    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("lastname")]
    public string Lastname { get; set; }

    [JsonProperty("cpf")]
    public string Cpf { get; set; }

    [JsonProperty("birthDate ")]
    public string BirthDate { get; set; }

    [JsonProperty("motherName")]
    public string MotherName { get; set; }

    [JsonProperty("postalCode")]
    public string PostalCode { get; set; }

    [JsonProperty("adress")]
    public string Adress { get; set; }

    [JsonProperty("adressNumber")]
    public string AdressNumber { get; set; }

    [JsonProperty("complement")]
    public string Complement { get; set; }

    [JsonProperty("background")]
    public string Background { get; set; }

    [JsonProperty("graduations")]
    public IEnumerable<Graduation> Graduations { get; set; }
}

public class Graduation
{
    [JsonProperty("instituionName")]
    public string InstituionName { get; set; }

    [JsonProperty("grade")]
    public string Grade { get; set; }

    [JsonProperty("formationYear")]
    public string FormationYear { get; set; }
}

Your Controller

[HttpPost]
public IActionResult Create([FromBody] RootObject obj)
{
   // Faz algo aqui 
   return Ok();
}

And finally have the long awaited result, hehe.