There are some tools available who can do this.
If you intend not to use any tool you may have to do something like this,Never done this though, but a thought. You can write a program in any language perl/java to select data from Oracle and then insert it into DB2 tables.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.