The variables available depend entirely on the data the trigger contains. The data provided in that trigger can be found below.
manual.joomla.org/docs/building-extensions/plugins/plugin-events/content/#oncontentaftersave
context = var1
item = var2
isNew = var3
data = var4
You should be able to access all the columns in _content from var2 as that's the table where Joomla articles are stored. To get the author user id you'd use [var2_created_by] which can be used in an Email action as the To recipient since it can convert user id to email address for you.