Atticus was never planning on letting King Calarian find out. Besides, even if he did, what was King Calarian going to do? He was no longer a match for Atticus; not even his entire kingdom's men banded together would be strong enough. Thus, Atticus had no care and merrily went ahead with using Calarian's pride and joy as training grounds for Daphne.
Of course, not that Daphne knew Atticus's true intentions. If she did, it would no doubt add yet another red to his ledger.
Thus, Atticus simply kept his lips tightly shut and made sure Jonah did so too. He didn't need his right-hand man to go around blabbing his morally gray plans to people who didn't need to hear it, not that he actually believed Jonah would.