What you would need to know is what TV channels are broadcast within range of your friend. "Within range" means that with a good antenna, oriented correctly, that the station can be recieved reliably, with enough strength (possibly with amplifier) to result in a good or acceptable picture. Television is usually broadcast on VHF or UHF frequencies. Antenna height and terrain are among the many factors that can impact the range.
Once you know what could be received if you had a good antenna then you can determine what to do. An alternative it simply to look at rooftops to see what everyone else is doing, what direction the antennas, if any, point or ask.
Tapping in to cable TV is likely to be against the law. The only hope you might have is to receive something that is leaking out. The problem - when it leaks out it's usually caused by a problem and causes other problems. Eventually it will get fixed and the "free" TV goes away. It would seem that any effort in this direction just isn't worth it.