Xué. The phonetic tone of the word "Xue" is xué, and Xue is a double pinyin festival, which consists of the initial X and the vowel ü e. The learned tone is marked on the letter E. This is because the pinyin of Xue is Xue, where E is the vowel, and the tone is usually marked on the vowel, so the tone should be marked on the letter E.