The official gallery of high quality examples is maintained in a separate repository:
https://lazarusa.github.io/gnuplot-examples/
The examples in this documentation are intentionally very simple, in order to focus on the package functionalities. The only relatively complex, publication-quality plot, is discussed in The cairolatex terminal section.
Keep in mind that Gnuplot.jl is just an interface to gnuplot, so everything you can do with the latter is achievable from Julia. Further gnuplot examples can be found here: