Great question!

eNotes can be cited as a "web publication." Discussion groups, blog postings and the like have been designated their own guidelines in the MLA handbook. You would cite an answer from eNotes' Q&A section according to this template:

Editor, screen name, author, or compiler name (if available). “Posting Title.” Name of Site. Version number (if available). Name of institution/organization affiliated with the site (sponsor or publisher). Medium of publication. Date of access.

For instance, this page could be written into your Works Cited as:

jessica-gardner. "How do you reference material found on enotes.com using in-text parentheticals and a Works Cited page using the MLA format?" eNotes. eNotes.com, Inc. Web. 24 May 2012.

Note that the last date is the date you accessed the material, not the date it was created.

An in-text reference would look like this:

(author's last name/screen name, "article title")

However, if only one article by the author is in the Works Cited, the article title can be left out of the in-text citation.