On the Casio website, you will find quick guides for Casio Calculators including the ClassWiz.
You can find an excellent calculator guide for the Casio FX991EX-ClassWiz on Dr Frost’s site.
For the complete manual from Casio see this page, note the calculator is listed under fx-570EX / fx-911EX on the Casio manuals page. Select this page for the direct link.
From Pearson-Edexcel, one of their excellent guides from the Teaching and Learning Materials collection, we have this guide to using calculators when teaching AS and A level Mathematics. This very clear 5 page document lists specification content for AS and A Level Mathematics and provides video tutorials for a Scientific Calculator (Casio ClassWiz) and a Graphics Calculator (Casio CG50).
Casio ClassWiz Teaching Videos.
Calculator Guide Classwiz resources.
Also from The Calculator Guide on YouTube see this comprehensive playlist on the Casio Classwiz fx-99EX. For example see this introductory video on using Statistics mode to find the mean, variance and other statistical summary data.
Other examples include further statistical videos such as Normal Distribution calculations, integration and differential calculations and using Complex mode.
David Smith – Playlist for Classwiz – including Binomial Distribution and Normal Distribution.
See also this playlist from Casio on the Classwiz FX 991EX.
Better than a manual for the Casio fx-991EX, Dr Jamie Frost has written an excellent PowerPoint Slideshow explaining what the various buttons do. Just select the button you wish to know about.
All Casio manuals and other resources can be found on the Casio website here.