Ha, I just answered your issue on https://github.com/JuliaGeo/NetCDF.jl/issues/124. In short; groups don’t work in NetCDF.jl, but do work in NCDatasets.jl, so it’s best to use that.
On a side note, it’s probably best not to simulateously post the same question on GitHub and Discourse. Others that didn’t know about the GitHub issue could have put time into answering here, not knowing it was already answered.