I can't help by: Jacki Cammidge, Certified Horticulturist
For one thing, I don't know what this plant is, or where you're growing it. Is it outdoors? Indoors? Under lights? In a sunny window? You haven't given me enough information.
There are several things that it could be, such as some kind of blister mite, or even being sprayed with some type of chemical, or even being in the way of window cleaning, and then the sun hit it.
You need to give me a lot more to go on if I'm to even make a wild guess.