The best resources to catch up to ASP.NET Core 3
Practical ASP.NET Core is a very popular open source project maintained by SilverKey's very own engineering leader, Dody Gunawinata. It contains over 260 micro samples for various aspect of ASP.NET Core 2.1, 2.2 and the latest version of 3.0 preview.
ASP.NET Core 3 is shaping up to be the most significant technology upgrade for Microsoft .NET Framework in years. Make sure that you plan for adoption for your existing and newly planned systems.