I've seen a few questions about the online QAE so I hope this helps.
There's a dashboard that tracks your progress leading up to the exam. It shows your performance by domain and score for each session.
There are a total of 1,001 questions (see the breakdown per domain below).
You can do an adaptive practice exam where questions are chosen at random from the entire database or you can do a customized session where you select a category and focus on an entire domain or a subcategory within a domain. You can look at a detailed progress report to see how you perform on each subcategory.
You can further customize the practice exams by selecting new questions (questions you haven't seen yet), missed last time seen (answered incorrectly on the previous attempt), or trouble questions (answered incorrectly on numerous attempts).