Is there a way to view which user changed what within Scoutbook?
From your unit page, click pack/troop/crew/ship reports > audit log report. It contains some of what you may be looking for. If you are looking for who marked requirements or awards complete/approved/awarded, those show immediately under the award or requirement.
For advancements, unit Admins can also Export / Backup a Scout Advancement csv file, which also includes names and dates of who marked items as completed, approved, and awarded.