Basic computer science foundational knowledge is paramount.
Strong foundational .net knowledge including Oao concepts.
Clear concepts on c# features.
Strong understanding of how asp.net/ aspnetcore request pipelines works, knowledge of inner workings will serve you well.
Clarity on action<>,func<>, anonymous functions, event, delegates
Parallel programming in .net including knowledge of thread safe data structures in .net.
Liq: you should know this very well.
Asp.net middlware , JSON frame works