Yesterday I actually found an earing with a diamond in it also
Im not really good at knowing if its real or not but I do know first way to be close to real, is if the earing i.e the stud itself is hall marked, no one would really put a real diamond on a bit of metal if it wasn't 925 Sterling or 9ct or 18ct gold etc, so that's a good start if its hall marked,,
Then next is to see if the diamond actually sparkles or if it has a rainbow effect, if it rainbow effects chances are its fake, if it sparkles well possibility it reals..
Im no expert but these are some tips that can help straight away when u find it to give u a little hope as I found out from an expert