Canvas does not have a wiki tool per se, but you can essentially create a course wiki by creating a Page and allowing students to edit that Page. At this time there is no way to grade student contributions to this "wiki" Page, so it is useful only as an informal study aid and not a formal course requirement.
Please note: Canvas does not give any warning that another user is editing a Wiki at the same time as you. From our testing it appears that if two users are editing a Wiki at the same time, it will only save the data that is submitted first. This means that users can, and probably will, lose a lot of data and waste time while editing group wikis. One possible way around this is for users to type up and save their wiki contributions in Microsoft Word, then copy and paste their contribution into the "wiki" Page. This way, even if their work is lost in Canvas it will not be completely lost and they can easily copy and paste the information again.