Use an underscore and not a period (e.g. [cb_myfield]). Please see the below tutorial regarding further substitution usage information.
www.allmysocials.com/directory/tutorials/item/233-substitution-usage
Moderators receive a new user registration email, or at least they should, which you can add substitutions to but it uses language strings instead of a parameter. The language strings in question are as follows.
_UE_REG_ADMIN_SUB
_UE_REG_ADMIN_MSG
Note the above already includes Name, Email, and Username. You can find information on language string usage within your CB documentation (downloaded from Advanced downloads section) and from the below link.
www.joomlapolis.com/cb-solutions/languages