There are a few different ways that you can tell what version of Windows you are running from the command prompt. The first way is to simply type in ver without the quotes and hit enter. This will give you a output similar to this:
Microsoft Windows [Version 10.0.10240]
(c) 2015 Microsoft Corporation. All rights reserved.
As you can see, this tells us that we are running Windows 10 with the 10240 build number.
Another way to find out your Windows version is by typing in systeminfo without the quotes and hitting enter. This will give you a more detailed output which will include information such as your OS Name, Version, Build Number, etc.
Here is an example of the output you might see:
OS Name: Microsoft Windows 8 Pro
OS Version: 6.2.9200 N/A Build 9200
OS Manufacturer: Microsoft Corporation
OS Configuration: Standalone Workstation