Jon: As a reward for staying on your diet, I'm going to allow you to have some sugar with your coffee today.

Jon: Let me rephrase that.

reward n. 獎勵  

stay on 保持,持續(xù)做某事  
He resigned as chairman, but stayed on as an instructor.
他辭去了主席的職位，但仍然做導(dǎo)師。

allow sb to do  允許某人做某事
My boss doesn't allow me to use the telephone.
老板不許我使用電話.

rephrase vt. 重新措辭, 改述
Let me rephrase the question.
讓我重述下問題。

【參考譯文】

喬恩: 作為你堅(jiān)持節(jié)食的獎勵，今天我允許你喝咖啡時加些糖。

喬恩: 我得重述下所說過的話。