Hard to tell the scale, but most likely, that is b-vent from a furnace and or water heater. IE it's your chimney. Could also be bathroom fan type vents, or from an otr microwave, etc. At any rate, you most likely have an issue with a flashing on the roof, or with the storm collar around the pipe just above the flashing.
To fix it, get up there with a tube of Black Jack, Black Knight, or Bakor or whatever brand of roof-cement you can find, and caulk the crap outta everything!