Are there practice tests from the Java 8 book that I should NOT use for passing the Java 11 exam? For example, I think the new feature of try-with-resources (now we can use previously initialized variables as parameters) might be conflicting from Java 8 to Java 11 exams.
Oracle add a number of new topics (annotations, security, modules, var, etc) so you'll definitely be missing some material if you rely solely on the Java 8 book for taking the 1Z0-819 exam.
Besides having more details, we also changed the structure of the Java 11 Practice Test book to be closer to the real exam. For example, questions in the Java 8 book always had 4 options with exactly one answer, and we tried to keep many of them short so they could be answered more rapidly. For the Java 11 book, though, we relaxed these rules and made them harder and closer to the real exam.
It wouldn't hurt to study the Practice Test 8 book, although keep in mind these books are very different. There may be some edge cases in Java 8 that aren't true in Java 9. For example, if we asked to select valid modifiers for interfaces in Java 8, private would have been invalid. Likewise, Java 9 allows effectively final variables in a try-with-resources statement so any Java 8 question that disallowed that would be wrong. That said, very few questions from our book would be completely invalid in Java 11.