looks to be a fungal disease known as Phyllosticta leaf spot. It is mostly cosmetic in nature and will not kill your tree. This time of year I would do nothing since leaves will be shed in  couple of months and nothing you can spray will make the spots disappear.

Rake up leaf litter this fall to reduce inoculum for next year. Wet, humid weather favors disease development, and conditions can vary year to year. You could apply a preventative fungicide next year as soon as you see the first spots so that you protect the rest of the leaves. 

More information and control recommendations can be found here: https://hort.extension.wisc.edu/articles/purple-bordered-leaf-spot/