On the off chance you do not have access to the code and/or want to determine the version of ASP.NET that has been deployed on a machine, you can do the following (from TechNet):
How do I determine which version of ASP.NET MVC is installed on my
system?
For MVC 4.0, MVC 5.0, or MVC 5.1 you should have deployed the
affected binary (System.Web.MVC.dll) with your application. Check your
application’s bin folder for the version of the binary. For MVC 2.0,
MVC 3.0, or MVC 4.0, refer to the Add or Remove Programs control panel
item for the version of MVC installed.
Use NuGet package MvcDiagnostics that you can install. Create an MVC "hello world" or some other basic program, then install this package. The installation will prompt for the project to add a file to. Confirm and you should see MvcDiagnostics.aspx added to your project. Right click on this file in the solution viewer, then choose "View in browser". You should then see a nice page with all your assembly information. Mine looks like the following:
Microsoft ASP.NET MVC Diagnostics Information
This page is designed to help diagnose common errors related to mismatched or conflicting ASP.NET MVC binaries. If a known issue is identified, it will be displayed below in red text.
For questions or problems with ASP.NET MVC or this utility, please visit the ASP.NET MVC forums at http://forums.asp.net/1146.aspx.
Environment Information
Operating system: Microsoft Windows NT 6.2.9200.0
.NET Framework version: 4.0.30319.34209 (32-bit)
Web server: Microsoft-IIS/8.0
Integrated pipeline: True
Worker process: iisexpress.exe
AppDomain: Homogenous = True, FullTrust = True
ASP.NET MVC Assembly Information (System.Web.Mvc.dll)
Assembly version: ASP.NET MVC 4 RTM (4.0.20710.0)
Full name: System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
Code base: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Web.Mvc/v4.0_4.0.0.0__31bf3856ad364e35/System.Web.Mvc.dll
Deployment: GAC-deployed
ASP.NET MVC Futures Assembly Information (Microsoft.Web.Mvc.dll)
An ASP.NET MVC Futures assembly has not been loaded into this application. A download for this version of ASP.NET MVC Futures is not available. Pre-release versions of the MVC Futures assembly are no longer available once that version of ASP.NET MVC has gone RTM.
All Loaded Assemblies
71 assemblies are loaded.
A_65e81fd0_eb37_47d8_aba0_baece822c7ad, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
Antlr3.Runtime, Version=3.3.1.7705, Culture=neutral, PublicKeyToken=31bf3856ad364e35
App_global.asax.1h_47vyd, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
App_Web_rnug5pva, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null
BasicAuthentication, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
EntityFramework, Version=5.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
Microsoft.Build.Framework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.Build.Utilities.v4.0, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.CSharp, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.JScript, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.VisualBasic.Activities.Compiler, Version=10.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.VisualStudio.Web.PageInspector.Loader, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.VisualStudio.Web.PageInspector.Runtime, Version=12.5.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.VisualStudio.Web.PageInspector.Tracing, Version=12.5.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
Microsoft.Web.Infrastructure, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
Newtonsoft.Json, Version=4.5.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed
SMDiagnostics, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Activities, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data.DataSetExtensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data.Services.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Data.SqlXml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.EnterpriseServices, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.IdentityModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Net.Http.Formatting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Runtime.Caching, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Runtime.DurableInstancing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Runtime.Serialization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Security, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.ServiceModel.Activation, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.ServiceModel.Activities, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.ServiceModel.Internals, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.ServiceModel.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Transactions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Web.ApplicationServices, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.DynamicData, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Helpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Http.WebHost, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Mobile, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Optimization, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Providers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.RegularExpressions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
System.Web.WebPages, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.WebPages.Deployment, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Workflow.Activities, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Workflow.ComponentModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Workflow.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.WorkflowServices, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Xaml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Xaml.Hosting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
System.Xml.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089
WebGrease, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
This is another way of finding the MVC version for ASP net CORE projects by adding small code to your Home Controller. Hope this will be helpful.
Go to the Project Controller folder, open 'HomeController.cs' file. In HomeController.cs file, there is an Index Method with the return type of ActionResult/IActionResults. Just change the Method type from ActionResult to string and write the code, given below, into that method.