Every probe does something different, so they support different variables. For example, the logmon probe montiors log files, and it supports a variable for the name of the log file monitored by the profile generating the alarm. That variable would not make sense in the cdm probe, which is monitoring CPU, disk, and memory.
Have you looked at the probe help for the cisco_nxos probe? Usually you can find a list of variables for a probe in one of two places. A list is often included in the probe help, or sometimes you can get a list of variables to appear dynamically in the probe GUI by typing a $ when entering a log message and then pausing. (The probe help might mention if this technique works, but I would probably try it even if the help does not mention it.)