.NET Core is a backend technology in a web development stack, while JavaScript, jQuery (and other derivative technologies, such as Ajax) are for the frontend.
If you are hands-on with JavaScript, why not go with Node.js?
Node.js[
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If you are hands-on with JavaScript and want to learn .NET Core for backend development, then I would suggest you start with C# (as a language) and then dive into the .NET Core ecosystem; best, go with .NET 5 as that would be the future, so you do not need to learn the older technology that is expected to change in coming years.
Get started with ASP.NET Core MVC | Microsoft Docs[
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Lastly, inside the .NET Core ecosystem, we have Blazor that is used for frontend development, so if you want you can learn Blazor to build the application frontend and then move to the backend part once you are familiar with .NET tools, C# language, and the deployment models.
Blazor | Build client web apps with C# | .NET[
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