How do I create a "Reassing" report?

Hello,

I wouldn't use audit reporting.  I would use Query Builder.  I would review these:

Windchill Reporting Resource

CS204338 - Query Builder Report to fetch the reassigned task's Status Description for Project Activity in Windchill ProjectLink

CS162802 - How to make a Query Builder report to fetch reassignment information of a promotion request in Windchill PDMLink

CS143170 - QML Report showing Reassignment History for Change Task in Windchill PDMLink

And finally, always a good place to start Resource for reporting - PTC Community

You're usually not going to find exactly what you need in the articles and community, but at least enough to figure out your own solution.