I'm not Sanford, but all of this information is contained in the Activity Log of a lead record.
I'd like to understand the use case. Marketo itself wouldn't make it easy to do this except through the API and coding to compare values and Data Value Was Changed entry.
Like Josh, I'd like to know the use case.
If there are just a few fields you want to manage, then use another field like LatestUpdatedAmongFieldsABC. Every time you get a Data Value Changed trigger for one of the fields, overwrite LatestUpdated... with the name of that field. Better yet, set the value to the
Then you can both match on the field name and know when it was updated, if that's interesting in another context.