بسم الله الرحمن الرحيم
That wig that has been fitted to the head through surgery and it cannot be removed from the head is in the ruling of a real limb of the body. While doing wudhu a person can suffice with doing masah (wiping) on it.
The second type of wig which can be easily removed and put on is in the ruling of a hat (topi). During wudhu it has to be removed and masah must be made on the head.
أفضل التطبيق العصري على مسائل القدوري
للمفتي محمد أشرف الاشاعتي
Vol.1 Pg.87