Reddit mentions of C# 6.0 Cookbook: Solutions for C# Developers

As others have mentioned, writing code is the best way to get exposure. But if you're a book guy like me then there are a lot of option out there that'll accelerate the process. You'd be insane to read all the following--these are just starting points that can accommodate different interests/tastes.

Having said that, I'll start with the one book that I think every C# developer should own:

Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries

... it's a good read, and it includes a lot of direct input from the designers of the C# and the .NET Framework. Microsoft has been really good about sticking to those guidelines, so you'll immediately get a leg up on the Framework libraries if you work through this book. (Also, you'll win a lot of arguments with your coworkers about how APIs should be designed.)

General knowledge books (tons to pick from, but here are some winners):

• Cookbook-style factoids: C# 6.0 Cookbook, 4th Edition
  
• But since you're coming from a lower level language, you might appreciate more details: C# in Depth by Jon Skeet (the Chuck Norris of C#)
  
• Scott Meyers-style content with good discussions of idiomatic C#: Effective C#: 50 Specific Ways to Improve Your C#
  
• CLR via C# goes deep into the guts of the language.
  
  Deep dives into specific features that'll serve you well:
  
  
• Concurrency in C# Cookbook is a good starting point to get productive with the TPL quickly, but I actually learned a lot more from the more prosaic Pro Asynchronous Programming with .NET.
  
• C# generics aren't as powerful as C++ templates, but Metaprogramming in .NET may provide some decent (though clumsy) workarounds.
  
  Note: I've never found a good LINQ book that supported how I actually use the feature. Coming from C++, you can probably just start off by thinking of the extension methods on Enumerable as a C# version of std <algorithm>... a good way to avoid writing raw loops. But if you're a performance-obsessed game dev then you'll probably want to use LINQ sparingly--it does have some overhead.