Jamieson, Fausset and Brown on Daniel 2:10

10. There is not a man ... that can show--God makes the heathen out of their own mouth, condemn their impotent pretensions to supernatural knowledge, in order to bring out in brighter contrast His power to reveal secrets to His servants, though but "men upon the earth" (compare Da 2:22, 23).

therefore, &c.--that is, If such things could be done by men, other absolute princes would have required them from their magicians; as they have not, it is proof such things cannot be done and cannot be reasonably asked from us.