Here are a few resources to get started with eventing:
Blazer's "Ultimate Tutorial" (FE7) (starting on page 142)
Event Assembler/Event assembler language.txt is a big text file listing all the defined event codes for all three games, and includes a little description for most of them.
Alternatively, if you need more details on how different event codes look like, you can simply browse the
Event Assembler/Language Raws folder.
If you're looking for a standard definition/macro, you'll want to look at
Event Assembler/EA Standard Library instead.