Go around the Park a bit. You'll find him. If not, check the safehouse first
Remember the Idiot demanding 5 Bits?
Push or Trick him, then the Don will demand you, then he will give you a job looking for a Catgirl, simply go back to the safehouse ask Cassie about the Don and leave, she would be gone after a while.
The Cassie rescue which is the most Stat-checks in one run, it has a up-to-date wiki already.