There are several auditing solutions in GP both built into GP and through ISVs like TitaniumGP and Rockton:
Activity Tracking (available out of the box): Allows for tracking virtually any table within GP to track such things changes to master data like items, customers, and vendors and transactions (sales transactions, purchase order transactions, etc). Audit information stored in a single table - SY03000
Rockton Auditor: Available from Rockton Software, which provides similar capabilities to Activity Tracking, but with more features and functionality with different implementation/architecture: https://www.rocktonsoftware.com/knowledge-base/how-does-auditor-compare-to-great-plains-activity-tracking/
TitaniumGP Remember: Available from TitaniumGP, TGP Remember is perhaps arguably a more user-friendly implementation of an auditing tool, accomplishing the same thing as Activity Tracking and Rockton Auditor, but with a reimagined user experience: https://www.titaniumgp.com/tgp-remember/