What's the quicket way to get Joomla? Books, training etc? You want to train 10 Mid-to-Senior level Java designers in Joomla.
If u are attempting to save your time, dont begin with official joomla documentation. Visit http://world wide web.scribd.com/search?cat=redesign&q=joomla and browse some short fundamental lessons for any fundamental understanding. Next, a great way would be to install Joomla on local machine and experiment for couple of hrs, setting up/modifying modules, components, setting up templates and etc. Practice and just practice makes learning efficient. Next, when you will need to go much deeper into specific subjects, start reading through more complex documentations, forums, attempt to understand Joomla in the code behind. You may even use video lessons for any fundamental understanding. Any designers will not have problems learning Joomla,as it is has fast learning curve.
a useful source of video lessons is Lynda
For after sales development, I love using the core components and analyzing them.
I've found which i get new a framework quickest by reading through lessons and watching video screencast.