Show established samba mounts

The answer should be a simple mount -t <fs_type>:

mount -t cifs

You will have the exact list of mounted smb filesystem (that is cifs type).

This option is available at least on Linux and FreeBSD.

On your server, command smbstatus lists the clients that are connected to the server. https://www.samba.org/samba/docs/current/man-html/smbstatus.1.html