To set the DC to
Gather Information, use a simple DC representing the availability of information about the subject. Adjust the DC upward if the PC Gathering Information seeks in-depth information. For example, if a character wants to Gather Information about a secret laboratory, you might decide that a common person wouldn't know much about it, but any scientist or corporate worker would, so learning basic facts uses the simple DC for trained proficiency. The location of the building is superficial, so discovering it might be DC 15 (the simple trained DC). Learning the identity of the laboratory's owner, however, might be DC 20 if the corporation is more obscure.