Wu Zhu had gone to Jiangnan while Fan Xian was on a diplomatic mission to Northern Qi.
When Fan Xian went to Northern Qi, Wu Zhu went to the Temple. Before Fan Xian left for Northern Qi, Wu Zhu had told him his plan. He was to delay the Great Grandmaster Ku He. Fan Xian would deal with the others below the Great Grandmaster. Thus, Wu Zhu went to the Temple to search for the missing Wu Zhu to help Fan Xian defeat the Qing Emperor. Therefore, when Fan Xian went to Northern Qi, Wu Zhu was at the Temple.
When Fan Xian went to Northern Qi, Wu Zhu went to the Temple. Thus, Wu Zhu was at the Temple when Fan Xian was on a diplomatic mission to Northern Qi.
Wu Zhu had gone to Northern Qi before Fan Xian had gone. Thus, Wu Zhu and Fan Xian went to Northern Qi together. In the end, Wu Zhu chose to go to Dong Mountain alone to recuperate. In the ending of " Celebrating Years," after Wu Zhu was injured by the Qing Emperor, he decided to go to Dong Mountain to recover. Under the influence of Ye Qingmei, Fan Xian, and the others, Wu Zhu gradually regained his consciousness and hoped to live a quiet life and separate from Fan Xian's family. Thus, Wu Zhu went to Dong Mountain in the end.
Fan Xian had gone to Northern Qi, but Wu Zhu's exact whereabouts were unclear. In the plot, Wu Zhu had been to Jiangnan, Danzhou, and Jingdou. According to Fan Xian's lines in the play, Wu Zhu might have returned to the Temple, but his memory had been erased. In addition, according to the other answers, Wu Zhu might have chosen to go to Dong Mountain alone to recuperate. Therefore, there was no definite answer as to where Wu Zhu had gone.
According to the information provided, Wu Zhu had already gone to Northern Qi before Fan Xian. Wu Zhu's goal was to entangle Master Ku Ke and prevent Ku Ke from threatening Fan Xian. After Fan Xian returned to Jingdou, Wu Zhu had his own things to do, so he left. He did not mention where Wu Zhu had gone.
During Fan Xian's diplomatic mission to Northern Qi, he had a deep master-disciple relationship with Fei Jie. Fei Jie was Fan Xian's master. He taught him medicine and poison techniques. Fei Jie was very concerned about Fan Xian's safety. When Fan Xian wanted to go to Northern Qi, Fei Jie could not stop him. However, he expressed his worry for Fan Xian and said that if anything happened to Fan Xian in Northern Qi, he would let the entire Northern Qi be buried with Fan Xian. This showed Fei Jie's deep feelings and desire to protect Fan Xian.
Based on the information provided, it could be concluded that Wu Zhu had gone to Northern Qi before Fan Xian had.
Based on the information provided, it could be concluded that Wu Zhu had gone to Northern Qi before Fan Xian had.
Based on the information provided, it could be concluded that Wu Zhu had gone to Northern Qi before Fan Xian had. Thus, Wu Zhu and Fan Xian went to Northern Qi together.
Based on the information provided, it could be concluded that Wu Zhu had gone to Northern Qi before Fan Xian had. Thus, Wu Zhu and Fan Xian went to Northern Qi together.