I'm finished with all my hats..

You get 5 cookies for talking to a Suspicious NPC and 4 extra if you answer the question correctly.
Once they are talked to they dissapear and drop a basket which 3 extra cookies can be obtained.

This means that you will get a total of 12 cookies if your lucky.

There are about 3-4 scattered around town and 1 in each guild. They respawn approx every 5 minutes from the hours of 20:00 to 03:00, Night time ends at 04:00 but they never spawned after this time.