The default wiki comes with a FileSystemProvider which stores the content of wiki pages on the filesystem as specified by jspwiki.properties property jspwiki.fileSystemProvider.pageDir.
The default location of these files is:
Do this by updating (or creating) the <tomcat>/WEB-INF/classes/jspwiki-custom.properties file and adding the following content:
jspwiki.pageProvider = VersioningFileProvider
You then need to restart tomcat for this to take effect.
Now each time you edit a page a new version will be created. Go to the Info tab to see the different versions.