If we're talking about an ASP.NET app, the most important thing to log would probably be request URLs over time. You could either write custom middleware that

If we're talking about an ASP.NET app, the most important thing to log would probably be request URLs over time. You could either write custom middleware that dumps this to a file or database, or you could install Application Insights and get into the azure ecosystem a bit. I'm not a fan of App Insights but it is Microsoft's own technology and it does cover a lot of bases.