If your questions aren't answered in this help file, the skim-users mailing list may have an answer. Your question may have been answered already, so you can check the list archives to get instant gratification.
You can submit a bug report to the bug tracker at https://sourceforge.net/projects/skim-app.
The reports are most useful if they provide a clear description of what went wrong, what you expected, and how to reproduce the problem at a different computer without you there helping us.
If you're submitting a problem with how it handled a certain file, it would help if you sent that file too. Crash reports are also useful and can be obtained from the Console application (in `Applications/Utilities`).