So I am trying to do get the key for a model object in the controller so that I can add a AddModelError to it.
In my view I use
@Html.V
ModelState.AddModelError("Email", "the email is invalid");
But usually that's not something you should be doing manually in your controller but you should be using a validator. For example you could decorate this Email property with some validation data annotation attribute or if you are like me use FluentValidation.NET => this way you shouldn't be asking yourself questions about keys but focus on the actual validation logic.