The scaled coordinates range from 0 to 1. Left top is {0,1}, center top is {.5,1}. Then you may have to adjust the offset:
Text[Style["(b)", FontSize -> 14, Black], Scaled[{0, 1}], {-1, 1}]
Text[Style["(b)", FontSize -> 14, Black], Scaled[{.5, 1}], {0, 1}]
Confusingly enough, the offset range is from -1 to 1.