There is no direct or concise way to get the list that you are asking for.
From the clients you can use - "showmount -e <ipaddr_NetApp Storage>". This will list all the mounts upto 10000 entries.
From the NetApp Storage you can possiblely this information at one single point of time from the access cache contents.
The volume "test_vol" is exported out from the /etc/exports as follows:
fas6080c-svl13*> exportfs -c 172.17.39.72 /vol/test_vol -ro
exportfs: 172.17.39.72 has ro access to /vol/test_vol