Summary:
'Exchange Rate' has been checked within 'Expense Columns' under 'Expense Setup' and the 'Exchange Rate' option has been checked within 'Settings' in a Expense sheet. However, I am unable to view the 'Exchange Rate' column within the Expense sheet.
 

Solution:
'Exchange Rate' column is visible within an Expense sheet only if the currency within the 'Net Amount' column is set to a different currency other than the base currency. For Example; If the base currency is set to USD$, and the currency within 'Net Amount' is set to USD$, 'Exchange Rate' column will not be visible. Now, if the currency within 'Net Amount' is changed to CAD$, then 'Exchange Rate' column is automatically launched.