What do you expect to be obvious, before you have learnt it? (Agreeing with dchall8.)
This is not about intrinsic fields (you're right, they don't exist in 9), but about function names, isn't it?
Anyway, in 9, all field names are shown in the Schema dialog where you make an expression, and also in the table which may well be underneath. Or if you are making the computed field in an SQL command window, then all fields can be shown in the tables panel with just one drag from the Project pane.
But getting back to functions. Their names are more "obvious" in 9 than in 8--once you have learned and practised a bit--for 3 reasons. First, naming is systematic. If it is a geometry function, it starts with Geom; an image function starts with Tile; a text function starts with String, and so on. Secondly, expressions are just SQL. you learn a new piece of SQL9 syntax once, you can use it everywhere. Same functions, same syntax. Third, there is a query builder, with a comprehensive list of all the syntax you need for queries, right in the UI. Just press Ctrl-~. Similarly for the Expression tab for Contents > Transform. In both cases you can just double click, hardly any typing required. ...
Could something similar be added for the Schema dialog, to give a handy reference when writing the expression for a computed field? That could make a good suggestion, especially at the moment since Adam has mentioned there are already plans for a redesign of the Schema dialog.