in millsberry, where do you find Robert J. Williams?

Answer 1

You can find his house by typing in robertjwilliams in the address book. It will return several entries but the one you want is Robert J. Williams in lakeview.

But if you are looking for information about how to send him a postcard for the karate task then you want to:
Go to the post office (http://www.millsberry.com/post_office/)
Click on "Send a Greeting"
Select the "Thank You" category.
Select one of the "Thank You" cards.
In the recipient name area type in robertjwilliams (just as it's written there, no punctuation, no capitals)
Cick send

Do not change the name in the "from" box or it will not register that you've sent the card.