Citrus black spot appears on the fruits and the lesions eventually spoil them: that's why it's such a devastating disease for commercial orchards.
Try to see if those dots wipe clean with a damp cloth. If they do you can just forget about them. If not it's most likely melanose: it can be managed by applying a copper fungicide, albeit now it's a little late for eradication and will only keep the disease at bay until flowering season.
