You can use the Diplomacy skill to gather information about a specific topic or individual. To do this, you must spend at least 1d4 hours canvassing gathering places in a district. The DC of this check depends on the obscurity of the information sought, but for most commonly known facts or rumors it is 10. For obscure or secret knowledge, the DC might increase to 20 or higher. The DM might rule that some topics are simply unknown to common folk.