Object Oriented programming is a paradigm, not a technology. Different technologies follow this paradigm, like C#. There exist dozens of different paradigms, which basically are different approaches to solving problems.
LINQ inherits concepts of functional programming to make your life easier where pure OOP falls short. Learning this technology is a must if you are a C# developer.
WCF and WPF are part of the .NET framework to solve particular common scenarios. WCF can be used for networking, while WPF can be used to create visual applications. Obviously, if you aren't creating an application which does any form of communication with external applications, there is no need to learn/use WCF. Likewise for WPF, there is no use to learn it if you don't need any visuals. Alternatives exist for both WCF and WPF, but given they are frameworks supported by Microsoft they are often a good choice.
Even experimental alternatives to LINQ start to pop up, e.g. Push LINQ. These are far away from completion, and you are probably better off sticking to ordinary LINQ for the time being.