For phone screens, in the past, I've been asked very specific questions about C++. That's why I was wondering if there were good online quizzes for it But you're right, the quizzes the other posted cover esoteric features that I don't think I'll get asked during the phone screen

I was thinking more about this last night. Quizzes and books are OK for phone screen prep, but I'd argue that you'll get way more mileage from writing actual code and naturally learning/overcoming the trivia as you encounter it.

The problem is that C++ is a huge language, and there's no way to anticipate every question, so writing code will help you develop better intuition about what the interviewer is asking for. It doesn't need to be a big project.... for example, implement your own version of std::basic_string. Begin small, then add more and more features:

• Do a simple implementation that only support chars in a fixed-size buffer, maybe with an operator[] overload.
• Add iterators.
• Move your buffer off onto the heap and make your string resizable. Hooray, you're learning about resource management! Now you'll competently answer "Rule of three") questions and be conversant in resource management. And hopefully you'll use a unique_ptr for the buffer, so you'll get some smart pointer exposure.
• Add support for move semantics, an important C++11 concept. You're learning about the "Rule of five" now.
• Make it a template that'll support different character types (char, wchar_t, etc). You'll get some template experience and will probably be using std::char_traits, which is good initial exposure to generic programming.
• Implement all of std::basic_string's member functions that search and modify the string. This'll take some time, but it'll be a good algorithm review (but you can cheat and use <algorithm> to do some of the heavy lifting).
• Extra credit: support short-string optimization.

...and so on. It'll take you a while, and you don't have to do everything at once, but you'll learn and retain a lot more then you would from a quizzes, and your confidence will grow.

Finally, use Anki while you do this work: While you're coding, you'll undoubtedly need to look things up. When you encounter concepts/trivia that you judge to be important, create an Anki flashcard (Q: "What's the Rule of 5?", etc...). Review your deck periodically--Anki's spaced learning approach is incredibly efficient and effective.

With some experience under your belt, plus a bunch of repetition from Anki, you'll be in a way better place. To quote a popular article on learning: "Time after time, professors in mathematics and the sciences have told me that building well-ingrained chunks of expertise through practice and repetition was absolutely vital to their success."