This seems to be a fairly competent intro to DataFrames.jl https://github.com/sylvaticus/juliatutorial
Didn’t seem to get much attention. Of course there is also https://github.com/bkamins/Julia-DataFrames-Tutorial which I have contributed a tiny bit too.
And I think the wikibook one is meant to be decent as well Introducing Julia/DataFrames - Wikibooks, open books for an open world.
Any others?