Go to Data Source.
Click the following button and select data source order.
The calculated fields will be at the end.
You can right-click on the fields to get the actual calculation.
I don't know of a way to get them as a simple spreadsheet-like listing.
The .tbw is XML, so you could bring that into a text editor (or better, write a program to read/search) and look for 'formula='. Actually, you could copy the whole thing into excel, read it into Tableau as a 1-column file, and then use string functions to find the set of formulas...