-o Object instance for which data is to be retrieved. Multiple object instances can be specified. Specifying a parent will retrieve data for all its children.
-C A counter of the form object-name:counter-name (ex. system:cpu_busy). Multiple counters can be specified.
So in your case, the CLI would be something like "dfm perf data retrieve -o yourvolumename -C volume:cifs_read_latency". Note that you don't put the volume name in the counter parameter. You can put multiple "-C" parameters on a single command line if you need multiple counters for the same object, for instance:
If you use multiple counters within a single retrieve another option to consider is "-x TimeIndexed" which organizes the output in a tabular format by sample time. If you specify counters that are updated on un-correlated schedules or if you specify multiple objects that might have uncorrelated collection schedules you may run into some odd results on a TimeIndex report, since DFM tries to make sense of all the data in a single aggregation.
To get the form of the volume instance names you need, run the command:
dfm perf counter list <controller>:volume:*:*:*:*
substituting the name of your 7-mode controller. If I remember right in 7-mode the volume name form is either controller-name:/volume-name or controller-name:/vol/volume-name, but the counter list command will display the form you need.