How to catch actual exception column in catch block

I have .NET project made with api's and I am calling these api in android app , Now I am getting error in android like object reference is not set to an instance of object i know it is due to null values I have deployed .net project on IIS so its deployed version Now I want to get the actual column where it is getting null values so it is throwing object reference is not set to an instance of object . 

i am using exception class like (Exception ex)

{

ex.Message

}