In a Freeform SQL report, there is no Report Filter window or filter object. However, there are two ways a user can view the filter details for a Freeform SQL report in Strategy Developer 9.4.x-10.x.
Option A :

NOTE: This requires the user to have 'Define Freeform SQL Report' permissions which uses a Desktop Designer license.
Option B:

NOTE: This requires the user to have 'View SQL' permissions which uses a Desktop Analyst license.