Visual Studio 2019 Debugging without Source Code

Visual Studio

• Decompile the dll with ILSpy, find the function you need.
• Attach to Process: w3wp.exe - your application's pool
• Debug -> Windows -> Breakpoints.. -> New -> Function Breakpoint: Type the function name with the namespace you found.
• See the variable in Local window.

DotPeek Plug-in for VS

Tools -> Options -> Debugging -> Uncheck Enable just my code
Tools -> Options -> Debugging -> check Suppress JIT optimization on module load (Managed only)

DNSpy

• A standalone Debugging IDE.

References

• https://michaelscodingspot.com/dotnet-debugging-tools/
• https://michaelscodingspot.com/debug-3rd-party-code-dotnet/