Session statistics can be obtained by running  the NX Session Administrator GUI. 

To do that, start an NX session, then right after that, start the NX Client Administrator GUI (/usr/NX/bin/nxclient --admin) on the same client machine,

Run the session for a while, then open Session --> total/partial statistics. You will see the relevant statistics for that session.

The statistics can either be copy/pasted out of the popped up window or can be viewed in the users homedir in .nx/S....../stats file.

To obtain the partial statistics, i.e., the statistics accumulated since the last time you clicked on the button, select the icon on the toolbar representing a histogram with a clock.

To obtain the total statistics, i.e., the statistics since the beginning of the session, click on the graph icon being on the right, the one without the clock.