The Aws Sct tool only supports DB2 LUW as a source  , not as a target database.    A typical scenario may be AWS SCT DB2 LUW to PostgreSQL migration 

To setup a source connection to a DB2 LUW server and database

Step 1 : Download valid drivers to connect to the server and connect to the database . This link will take you through to an AWS page listing links to drivers sources . Look for the Database Engine - IBM Db2 LUW.   Drivers - db2jcc-db2jcc4.jar

Downloading the required database drivers 

Step 2: Add the correct file path reference in the AWS SCT Global Settings for the DB2 driver path 

Step 3:  Privileges for DB2 LUW as a source  & Connecting to Db2 LUW as a source    use this link to the AWS site  to detailed information 

Using IBM Db2 LUW as a source for AWS SCT

Useful links 

Dive deep into database migration services AWS DMS and AWS SCT