Dust during printing will appear white on the print; dust on the lens will appear black.
It could also be slight "scum" which you can feel on the print's surface although when I worked in a lab, this was a very rare occurrence.
D***** is even worse for dust! As an assistant, I kept the lenses scrupulously clean, but dust would always find its way onto the sensor; after every shoot the camera would be sent for cleaning.
Inspect your negatives - if you can see white on them in the same position as the print, it's dust at the time of exposure.