Hello,
Run a listvtoc for the volumes you are interested in monitoring.
If you want to look at a/some volumes only once in a while, you can use tso/ispf 3.4, specify V and the volser you want to monitor. This will be returned:
Unit . . : 3390
Volume Data VTOC Data Free Space Tracks Cyls
Tracks . : 50,085 Tracks . : 70 Size . . : 11,948 792
%Used . : 76 %Used . . : 3 Largest . : 7,425 495
Trks/Cyls: 15 Free DSCBS: 3,420 Free
Extents . : 28