Just my two cents...

These stuff are pretty basic.

For DDS, I think you only have to remember a few key letters...dili keywords...key letters...

For CL, You will learn more of it as you get acquainted more with the AS400.
Like all scripting language, it is very straightforward.

For RPG, naa ra gyud sa akong atubangan ang code wala lang gyud ko ni-try. Basically, a reporting language.