Translation:That test is not difficult.
I think the usage of "the" in English is flexible enough that it could be any of この、その or あの、or none, depending on context. Translating その as "the" is probably valid most of the time, but translating it as "that" is probably valid in an equal number of cases. Duolingo hasn't exactly been consistent about it; they often require it to be "that" only.
I thought about why I might say "that" versus "the" test in normal speech, and I feel like they're almost interchangeable, maybe depending a bit on whether me and the listener are taking the test or talking about a test someone else is taking. Lacking any context, I think both are valid. I might even say "this".
No and yes. In thise case, sono is used to talk about an event or ideal. If kono was used I would assume I run the class and I don't think it's hard. Sono means I may have taken the class, I may not have but I have some experience with it that allows me to know that it is not hard. Ano would mean I'm purely speculating on wether or not the class is hard because I do not have first person experience. Very complicated consept
Ultimately it always boils down to context, because that decides a lot of things in actual conversation. These random individual example sentences obviously can't all have entire paragraphs for context, so we often end up with issues like this. As such, it would indeed be more fortunate and less confusing (especially on this beginner, supposedly-N5, level) to stick to the most direct, primary meanings/usages of words...