Did you check the homestead chests, backpacks and other containers in your characters' inventories, etc? There is a pouch container that has the same icon as a pouch of bonedust or moondust. If any characters were arrested since getting the scroll, check the Evidence Chests in the Legion headquarters.
Check Evelyn's house, as well, in case you ended up reloading an earlier save for some reason, and didn't re-loot it from the chest.

If there are a limited number of places where you may have been sorting your inventory, checking there with the Alt key pressed could help find it (X in the Linux version, or with Show World Tooltips toggled on using a controller). For example, a couple of people have dropped the scroll around the fountain near Evelyn's house, one at the top of the stairs leading to the crafting station behind the blacksmith's abandoned house, one in the Hall of Heroes near the whetstone and another in a backpack left in the Hall of Wind.

​Did you check older saves, if available, until you found the most recent one with the scroll, and oldest without? Knowing when it went missing could help narrow down where it may have been dropped, etc.

If you can not find the scroll, and are playing on PC, please email supportdos@larian.com with your latest save (or a Dropbox or Google drive link, etc).
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin Enhanced Edition\PlayerProfiles\<ProfileName>\Savegames_patch' folder (and similarly in OSX; in Linux they are in the home directory).
In Windows Explorer you can zip a file or folder by right clicking on it (or them) and selecting 'Send To | Compressed (zipped) Folder'.