There are a few ways to approach this.
1. There is a FileTransfer event, you can subscribe to that, this works when the Copy command is used.
2. There is a REST API (all thingworx content is automatically available as rest), so if you are making changes etc. You could chain a rest call to then execute processing of said changes.
3. A Timer, not too sure what exactly you are looking for, but if you use a timer, then you will need to go to the necessary repositories, retrieve the content details and somehow determine new, old, changed, removed etc. I don't think you will find a trail anywhere unless you create it yourself (store snapshots in a DataTable potentially)