Could aliens watch Earth TV signals?

Yes in principle, but in practice it would be extremely hard unless they are nearby and have very advanced receiving equipment.

Earth’s broadcast TV and radio signals leak into space as electromagnetic waves traveling at light speed. That means the earliest TV/radio leakage has reached roughly 100 light-years away by now, so any civilization inside that bubble could theoretically detect that Earth is artificial-radio-active.

But “watching Earth TV” is much harder than merely detecting a signal:

• Signals get extremely weak with distance because they spread out over space.
• TV broadcasts were aimed at local viewers, not beamed toward stars, so much of the useful signal is not strongly directed into space.
• Decoding the program would require knowing the modulation, format, timing, language, and filtering out noise.
• Modern TV leaks less into space than older high-power analog broadcasts, because much viewing now happens over cable, fiber, satellites with directed beams, or low-leakage digital systems.

A nearby alien civilization with a radio telescope far beyond ours might notice that Earth emits artificial radio signals. Actually watching old episodes of Earth TV from many light-years away would likely require an enormous antenna array and excellent signal processing. Stronger, intentional or radar-like transmissions would be easier for them to detect than ordinary TV broadcasts.