WeaponMaster

This tells you what weapon skills are usable and where and when they're trainable when you mouse over a weapon you can't use yet. This has to be explicitly created for each possible place in the UI a weapon tooltip can exist, and in the original release included only the inventory. This has been expanded to quest rewards and merchant frames as well. More to come in the future.

Also gives you access to the database of weapon trainers, classes, and weapon skills, and how those three relate.

To access the command line options, type /weaponmaster or /wm.

To perform a query, type "/wm" and a weapon skill, class name, or trainer name. e.g., "/wm warrior" and it will tell you all the weapons a warrior can use.

Say you then want to know where to train guns. "/wm guns" will tell you all the classes that can wield them, and who in your faction trains them, and where those trainers can be found. You can even query for data from the opposite faction!

There will shortly be a "self" report that will highlight any trainable skills that you personally have not yet trained.