That is a leaf spot disease, most likely Septoria. Possibly Tubakia leaf spot or Anthracnose. Anthracnose is less a "spot" and more of a disease that follows the veins, so that seems unlikely.
In general, these diseases don't hurt your tree much except to defoliate and make them less attractive. By the time you see the spots, it is too late to treat, anyway. These infections can be somewhat prevented or reduced in severity, but usually are not worth the trouble to spray for. Watch it for now, compare to next year's outcome, and then decide if it is worth the money to do preventative treatments.
You should be able to find a local arborist capable of giving you an appropriate treatment plan, along with prices. Doing it yourself is seldom a viable option, because most people don't have the right equipment to get adequate penetration of the fungicidal spray into the canopy of a tree.
Here are some systemic fungicides that have shown promise in managing these leaf spot diseases:
Propiconazole:
A broad-spectrum systemic fungicide
Effective against all three diseases: Tubakia, Anthracnose, and Septoria
Often used as a preventative treatment
Thiophanate-methyl:
Systemic fungicide with broad-spectrum activity
Particularly effective against Anthracnose and Septoria
May also provide some control for Tubakia
Azoxystrobin:
A strobilurin fungicide with systemic and translaminar activity
Effective against all three diseases
Often used in combination with other fungicides for better resistance management
Tebuconazole:
A triazole fungicide with systemic action
Effective against Anthracnose and Tubakia
May provide some control for Septoria
Myclobutanil:
Another triazole fungicide with systemic properties
Effective against Anthracnose and can help manage Tubakia and Septoria
I don't ever recommend treating for leaf spot diseases as my customer base doesn't care enough about cosmetic appearances, so I cannot make any recommendations for you. My business doesn't revolve around my spray applications, so any advice I would offer for a treatment plan would probably be flawed.
I sprayed a bunch of trees two days ago, but that was to
give them some leaf spots. Big, leaf dropping spots that would defoliate and kill the tree along the way. The plan was to wipe out the underbrush and understory trees, while leaving the bulk of the tree thicket intact so as to discourage homeless encampments.