You can query on Online Express Comments with either a Constituent or Gift Query.
  1. Create a new constituent or gift query
  2. On the Criteria tab click the + next to Gift Information (if Constituent Query) or Gift (if Gift Query)
  3. Scroll down and locate Attributes, push the + next to it
  4. Scroll down and locate Specific attribute, push the + next to it
  5. Scroll down and select Online Express Comments > Online Express Comments Description
  6. Set the operator as Not Blank or however the client would like to search
  7. The Online Express Comments Description should be included in the output, if not include it.