I'm a bit stuck at the moment but still looking for the answer myself (though I need one by tomorrow morning). I've just been asked to produce a report (or output - CSV or any format should be acceptable) on all of the searches run in DA by a particular user.
It looks like the built-in DA reports contains an option for type "Searches" but when I go to add a value, only the searches conducted under the account I am logged in as (the Vault Service Account) are returned. I don't understand why the Vault Service Account, which I've given every possible persmission, can't add the searches from all other DA users that have been conducted. I would imagine if I could log in as the user I need to report on (which I cannot, by the way), I would be able to generate a report on their searches.