[HttpPost]
public class StudentController : ApiController
{

    public void PostSomething([FromBody] string name, [FromBody] Student s)
    {
        //do something
    }
}

{
    "name" : "John",
    "student" : {
        "id" : "1",
        "age" : "22"
    }
}

{
    "John",
    {
        "id" : "1",
        "age" : "22"
    }
}