For the parties that you are setting up to be merged in a merge batch, you can view the merge-from and merge-to parties' profile information. See: Merging Parties.
Party profile information differs depending on whether the parties to merge are organizations or people. You can see the taxpayer ID and tax registration number for both, but the date of birth for parties of type Person and the D-U-N-S Number for parties of type Organization.
Navigate to the Person Profiles or Org Profiles tabbed region after you enter the basic merge batch information. See: Merging Parties.
For either the person or the organization, you see the profile of the merge-from party that is to be merged with the profile of the merge-to party.