The DOD, JPL, NASA, NOAA, and others do track space debris. The debris the ISS is mainly worried about is microdebris, and others of similar sizes. The companies/organizations listed above do track debris using radar, laser ranging, optical, etc... Most large debris (i.e. R/B, S/C, etc...) are well tracked. The debris sizes around 10 cm^3 or or laptop size are slightly more difficult but are still tracked to some degree of uncertainty. All tracking is done from the ground at ground stations. Some objects can be tracked from other spacecrafts in orbit, but it is usually not the case.
Also most debris locations are around an inclination of 71 to 98 degrees. Currently there is about a week notice before a possible known collision with 10^3 cm to larger objects. The ISS does have features that detect incoming debris or smaller objects.
ISS Debris Detection: http://ieeexplore.ieee.org/document/879836/ and http://www.esa.int/esapub/bulletin/bullet109/chapter16_bul109.pdf
ISS Collision Maneuvers: https://sma.nasa.gov/news/articles/newsitem/2015/11/23/two-more-collision-avoidance-maneuvers-for-the-international-space-station