This calculation(s) uses parameters and table calculations to find the desired Nth value from a list. This example uses Superstore. It is important to note that the values are based on the Customer field that has been sorted in descending order based on sum of Sales.
//Create an integer parameter that starts with 0 (in this example the parameter is [Return Nth Value])
if index()=1 then
WINDOW_MAX(sum([Sales]), first()+[Return Nth Value], last())
Inputs and Setup:
Place the above calculation on the text shelf. Place the desired dimension (in this case Customer) on the level of detail shelf.
Partitioning and Addressing:
Set the above calculation to Compute Using>Customer (or applicable dimension).
Adopted from Joe Mako's example found here: