This kind of stuff is always highly individual both on an all time and based on recent programming basis.
Typically when training with adequate rest 6-8 sets per session up to 2-3 times per week (12-24 total weekly sets) on average (different individuals may require different approaches).
*If you haven't done higher frequency or volume is below this don't jump in too high too quick, start low and build.
**Vary these things one specific volume will produce different results even for the same individual based on circumstances.
***Periods of higher targeted volume and frequency for lagging parts can work well if you lower volume in other areas.
Finally keep in mind this only matters or makes sense if you are actually getting proper muscle activation and intensity for the required muscle.
I personally do 0 direct work currently.