According to ICV2,

The upcoming Watchmen Companion collects pages from Who’s Who in The DC Universe, featuring the Watchmen and the Minutemen characters; and reprints The Question #17, guest-starring Rorschach, and a page from the promotional DC Spotlight #1 from 1985 that marks the first appearance of the Watchmen in print.

The Watchmen Companion also includes the Watchmen Sourcebook, along with the Watchmen: Watching the Watchmen and Watchmen: Taking out the Trash game modules, from the DC Heroes Role Playing Game. The RPG material was sanctioned by Alan Moore and includes illustrations by Dave Gibbons, expanding on the lore and world of the Watchmen series.