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 https://en.wikibooks.org/wiki/Introducing_Julia/DataFrames#targetText=DataFrames[edit],set%20of%20related%20data%20values.
Any others?