You can find gifts for a specific constituent on the Gifts grid in the Fundraising Module or in their constituent record under their Gifts tab. 

From the Gifts Grid you can search by Last Name and add additional column filters, like First Name, to narrow down the list.

From the Constituent’s Record, click on the Gifts Tab to view all their transactions. You may need to check the boxes at the top of the grid to view Memberships or Soft Credits if desired.