I am preparing for the cissp certification and am thinking of getting the study guide for exam in dec 2020 or early 2021. However the guide edition 8e came out in july 2018. Should i go ahead and order the book or will there be a newer edition coming out soon?
ISC2 certifications are typically updated on a 3-year cycle. The CISSP was last updated in April 2018, so any study materials released after then should be covering the current version.
BTW - the major concepts the CISSP curriculum is based on don't tend to change from version to version, so don't get too hung up on your study materials not having been published in the last 5 minutes!
Outside of minor revisions most of the information is well enough and up to date for studying for the exam. Be sure to read as much as you can find in the bibliographies as web based sources tend to be the most up to date information. Sources such as anything having to do with the NIST or other US Federal Government will always be up to date. Same with encryption, things like that.
Last keep in mind that all books are considered 6 months out of date from publication. Hence the reason to keep up to date with the bibliography. Just be prepared to occasionally know two sets of facts and what year they may have changed. For example OWASP Top 10 is updated every 2-3 years and often changes slightly. Know the basic changes to the year in case you see a question or two that looks wrong but just out of date. This is true of all IT based exams.