The action icon is a great shortcut to easily choose the kind of transactions you'd like to make in QuickBooks Online. You're right that it's no longer in the upper right-hand corner of your page, but it's not gone.
With the changes being made to the program over the past several weeks, one of them has been reconfiguring the interface of the program. The action icon is now available in the left-hand menu of your QuickBooks account and it's called +New. There, you'll see all the same transaction options, including journal entries.