Which wiki are you talking about, Soul Knight Wiki? If so, you cannot. The "Discussions" on article pages is actually a feature of Forums, not Discussions. Since the Soul Knight Wiki was created after November 2016, it does not have and will not be allowed to enable Forums. The Warframe Wiki, although it has Discussions, appears to be among those that were permitted to keep Forums as well. Although it is my understanding that, officially, those that switch to Discussions are supposed to have Forums disabled, apparently Wikia has been making exceptions.