This question is very similar to Setting the version number for .NET Core projects, but not the same. Using the latest stable version of .NET Core at the time of writing (1.
I use Jenkins + Octopus for CI, and following worked quite well:
Powershell script that can take CI build number as a param or default to something preset. nuspec file in the project for CI.nuspec file with the latest build version.Nuget manually with a nuspec file from #2.nuget package to Octopus.