Kahootz logs the creation, modification and deletion of every object, and document downloads too. It also records every time people log in and log out, get invited to and leave workspaces.
Where can you see it?
Documents have an Activity section, which shows who has downloaded the document, made changes to it, uploaded new versions etc. This is only visible to people who can edit the document, not members who can only view it.
Workspace managers get access to Manage Workspace > Audit Log, which shows all activity in the workspace, ordered by time. There's a drop down to filter by item type to just show documents or calendars etc.
For enterprise customers, site administrators can see the complete system of audit logs (for all workspaces on the site) and all log ins and log outs etc.
The Kahootz support team are available to help if you have a specific issue and need to look into something in more detail.