There is not a report for this, but here is a script to give you the info. You can build this into a portlet or a custom report. You might want to modify this code to remove disabled users or add other fields.
SELECT ku1.full_name "USER", ku2.full_name Delegated_To, rd.start_date, rd.end_date
FROM rsc_resource_delegations rd, knta_users ku1, knta_users ku2
WHERE rd.start_date < SYSDATE
AND rd.end_date > SYSDATE
AND ku1.user_id = rd.resource_id
AND ku2.user_id = rd.delegated_to_user_id;
-- Remember to give Kudos to answers! (click the KUDOS star)