Thanks for the question. I hope you are able to attend the Webinar. As an initial matter, something is strange with your code. In response to this:
Query[All, KeyDrop["class"]]@titanic
You are getting an answer that is grouped by class. Perhaps you could submit your entire notebook.
One quick point, though.
KeyDrop[#class]& is not a correct operator. You can see this by running the following
f29 = Normal@titanic[[1]]
This gives us a single Association. If you now run
KeyDrop[#class]&[f29]
You get KeyDrop["1st"], which is not what you intend.
