Assuming they are on the same server, you could do any of the methods that people use to compare data in two tables - for example:
SELECT col1,col2 FROM DB1.dbo.TableA
SELECT col1,col2 FROM DB2.dbo.TableA;
SELECT col1,col2 FROM DB2.dbo.TableA
SELECT col1,col2 FROM DB1.dbo.TableA;If you have a number of tables and columns, it is possible to use INFORMATION_SCHEMA.TABLES and INFORMATION_SCHEMA.COLUMNS to generate the list of tables and columns and construct the queries patterned after the above query.