Yes. Your query could look like this:
FIND Client WHERE NOT(EXISTS Transaction WHERE (Transaction.Client = Client AND Transaction.MadeOn = ?'Transaction Date'))
This query will display a window to let the user specify the desired date. You can, of course, replace the prompt (the ?'Transaction Date' part) with a date that, for example, is an attribute of an object available in the context, or a function that produces result of type Date.
