How can I build a report that shows when a specific report has been run and when?

You can build a report using the OTBI Usage Real Time subject area.

Here's an example:

SELECT
  "OTBI Usage Real Time"."OTBI Report"."Report Name" s_1,
  "OTBI Usage Real Time"."OTBI Report"."Report Path" s_2,
  "OTBI Usage Real Time"."Time"."Report Start Date" s_3,
  "OTBI Usage Real Time"."Time"."Year" s_4,
  "OTBI Usage Real Time"."User"."User Name" s_5,
  "OTBI Usage Real Time"."Facts - Usage Metrics"."Report Execution Count" s_6
FROM "OTBI Usage Real Time"
WHERE
(("Time"."Year" = '2023') AND ("User"."User Name" LIKE 'USERNAME%'))