WebJobs 3.x targets .NET Standard 2.0. This means you can use it from a .NET Framework application or a .NET Core 2.x application, the choice is up to you. If you want to make a .NET Framework application that uses WebJobs, then follow the same guide but with a .NET Framework console app as the starting point (instead of .NET Core).
If you're planning on deploying this webjob to a webapp that is running a .NET Framework application, I think it makes sense to use .NET framework for the webjob too.
You can refer here for more details on Webjobs Host.
Webjob SDK Version 2.x
The JobHostConfiguration class has a UseDevelopmentSettings method that enables development mode. The following example shows how to use development settings. To make config.IsDevelopment return true when it runs locally, set a local environment variable named AzureWebJobsEnv with the value Development.
Please let me know if this helps.