As we all know Skype for Business is not listed as a SharePoint Content Source as such:
In addition to the most common Online scenario which is eDiscovery running against Skype for Business conversations
(eDiscovery of course uses SharePoint Search):
https://docs.microsoft.com/en-us/microsoft-365/compliance/ediscovery?view=o365-worldwide
Don't forget you can also:
- Use Skype for Business archiving to archive conversations to SQL Server
- Use SQL Server as a Content Source for your Enterprise Search (in either a Basic Search Center or Enterprise Search Center)