How often I use
I use C# daily since that is the primary development language we use at my workplace.
My skills with C#/.NET
There's always something new to learn in this stack because it has a deep set of native functionality. I work mostly on .NET MVC web applications, so I have good experience with the libraries used therein, as well as with Entity Framework. I can write simple and complex foreach loops. We use Ninject for dependency injection and I am able to set that up. I can write LINQ statements to fetch data, as well as using Where() clauses and walking the EF object. I have used both RESTful routing and a route table (in a Route.config) in projects (I prefer RESTful routes). I have written web API methods. I've used the System.IO library for saving, editing, and deleting of files on a server as part of a document service.
We are just starting to adopt .NET Core in my workplace, so I don't have a lot of experience with that yet.
I have also done a little development in WebForms and WinForms (in C# and VB), as well as WPF. I'm no expert here, but I can mostly get things wired up and working, even if I have to look some things up on StackOverflow.