How to profile trigger database performance impact
There's no separate "trigger performance impact"; trigger code is essentially compiled into the execution plan of the statement that causes the trigger to fire, so measuring average DML statement response time before and after introduction of triggers should give you a general idea of the impact.

Of course, triggered actions will certainly affect other workloads, not only the triggering actions. I'm sure your DBAs have records of baseline database performance that they can compare to what happens after the triggers are added (presumably on a test system). 

As to monitoring tools, DB2 is fully instrumented to provide detailed views of its performance from various aspects, using event monitors and monitor views/stored procedures, so you don't need to set up anything in addition to what's always there.