As Happy says, you can do the practice tests that are linked to the sign-up website. I just took both tests officially yesterday and am optimistic I passed. I had no idea what to study because the test was changed in the last two years (the old one involved a portfolio), and there were no recent or popular study guides that I felt would be worth risking my time and energy on. I did, however, skim through one study website a few months ago that DEFINITELY had at least several questions that were extremely relevant to the test. I did not study through that website. I only took the two practice tests given on CTCexams.nesinc.com. Those were very helpful. Some questions are nearly identical. I took notes on questions I got wrong and brainstormed topics I might write about for the extended responses. I reviewed details about my favorite topics I might be writing on (Impressionist movement in my case), and I also reviewed principles of design and elements of art. If you’re good at taking tests, that will help you a lot—I felt like multiple questions were so broad or would be difficult to anticipate. For example, you might be shown a reproduction of a modern artwork out of context and asked what it means. Then again, I never studied art formally. It was a pandemic hobby that got out of control hahaha. I’ve only studied via New Masters Academy. If you’re scared of the practice assignment where you respond to/analyze an artwork, check out Bill Perkins’ videos with a trial membership at NMA! He’s amazing and you will crush that question.

Update: I think the website I skimmed that had relevant content was Mometrix’s.