How can I get the file name of log file?

Just for Windows platform:

#if PLATFORM_WINDOWS
    FString LogFile;

    FOutputDevice* OutputDevice = FGenericPlatformOutputDevices::GetLog();
    if (OutputDevice != nullptr)
    {
        FOutputDeviceFile* OutputDeviceFile =
                static_cast<FOutputDeviceFile*>(OutputDevice);

        LogFile = OutputDeviceFile->GetFilename();
    }
#endif  // PLATFORM_WINDOWS