To try and learn something about possible vampire activity in an area, simply use the vanilla topic "vampires". This is usually unlocked when some NPC cites vampires in his dialogue, usually when talking about latest rumors or little secrets.
Of course, responses will differ based on a number of factors, first of all who you are talking to. Commoners are likely the less realiable; some outlaws in their lairs might know a lot about nearby vampire lairs, but getting them to talk about it instead of attacking you can be tricky, of course!
In general, if there's a vampire lair reasonably close to a settlement, people there will comment on it. You might need to ask a bit around before you find someone knowledgeable, though.

Vampires themselves will give you informations about their Clan (or bloodline, if they are rogue vampires living away from the Clan headquarters), even if you're not a vampire yourself.
You'll have to manage to talk to them, anyway: they will still try and attack you on sight!
If you can get them to talk, vampires will now also offer you to give blood to them.
If you do, there's a chance you'll get infected with their blood curse (this is mostly for roleplaying, so you may become a vampire without having to punch one in the face first).
Just bear in mind that dealing with vampires is still a dangerous business... though quenching their thirst means they will be less likely to attack you.