How to enable logging for smbd on macOS?
With macOS 10.15, the only diagnostic logging available for smbd is done by grabbing packets.

Apple Support told me the following:


  To enable elevated logging; 

sudo log config --mode level:debug 
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.smb.server.plist LogLevel -int 1
sudo /usr/libexec/smb-sync-preferences

  
  To begin packet capture; 

sudo tcpdump -Pi BSDname -s 0 -K -w /Library/Logs/smb.pcap

  
  To end packet capture; Control-C
  
  Disable elevated Logging:

sudo log config --mode level:default 
sudo defaults write /Library/Preferences/SystemConfiguration/com.apple.smb.server.plist LogLevel -int 0 
sudo /usr/libexec/smb-sync-preferences