Answered by Shaykh Faraz Rabbani
What is the ruling of wiping the neck in wudu?
1. Wiping the nape [‘the back part of the neck’ – Webster’s] is recommended. [Nur al-Idah, Durral-Mukhtar, Hadiyya al-Ala’iyya]
2. Wiping the front of the neck is disliked and an innovation. [ibid.]
As for the statement of Imam Nawawi that it is an innovation because the evidence for it is excessively weak, this was not accepted by many other hadith experts.
Among the wisdoms behind wiping the back of the neck is that it is from completely wiping the head, front and back.
And Allah alone gives success.