How to open hidden part of ascx file (.asp)?

Question

ASP.NET

Suppose I have some file with extension ascx (eg x.ascx).
At the top of this file there are various parameters for it (link to the main page, class for inheritance, etc.)
And at the end of this line there is a link to the hidden code with which this page works (Codebehind="x. ascx.cs").
Q: How can I open this hidden x.ascx.cs page if I only have x.ascx file on my PC?

Answer 1

There are 2 files, I have only 1, the question is how to open the second one (which I don't have), the answer is no way.