Here's my two cents:
Well, there are alot of courses and certifications -class room training as well as online trining.
Is it to make a training course package for new webmasters or for job requirements?
The basic skills would be something like this:
HTML/XHTML - the markup language itself
CSS - Style Sheets
JS - JavaScript (client side scripts)
WebDesign & Graphics
PHP/ASP/Perl - One or more (Server side scripts)
MySQL/Sybase/SQL Server - Databases
From there you may want to "specialize" in ecommerce, media (Flash etc) and so on and so on...
Also webmasters may be required to master special web developer tools or CMSs (Content Managament Systems) and server skills it always nice to know about too....
.... it all depends what you need I guess.
Best Regards
Jakob