Solution found.
netstat -ta | grep nfsd|grep ESTA|awk '{print $5}'|cut -d : -f 1
or
ss -rta | grep nfsd|grep ESTA|awk '{print $5}'|cut -d : -f 1
and show all my clients connected.
To show the directories opened and file used we can query the good old procfs
Supposing my client is identified by 215
cd /proc/fs/nfsd/clients/215
I see 3 files
ctl info states
on file info I can see the ip, port used, hostname of client
clientid: ******************
address: "192.168.0.2:850"
status: confirmed
name: "Linux NFSv4.2 myclient.host.example"
minor version: 2
Implementation domain: "kernel.org"
Implementation name: "Linux 6.1.12 #1 SMP PREEMPT_DYNAMIC Sat Feb 18 16:45:16 CET 2023 x86_64"
Implementation time: [0, 0]
callback state: UP
callback address: 192.168.0.2:0
the file state show file in use, permissions and other info
cat states
- ***********: { type: open, access: r-, deny: --, superblock: "00:18:4627", filename: "video/My vacations.mp4", owner: "open id:******************" }
- *********************: { type: deleg, access: r, superblock: "00:18:4627", filename: "video/My vacations.mp4" }