How could we search for life in TRAPPIST-1 It is possible to search for life from here, how?
What methods could be used?
It is possible to look for organic matter?
Could we know if there is life according to the components of the planets atmosphere?
As far as I know, and aside from direct communication, there's only one way to "find life" on another planet. That method is to look for molecular oxygen in the atmosphere. Molecular oxygen hates existing by itself and loves to combine with other atoms and molecules through oxidation. The Earth's atmosphere is currently ~30% $\mathrm{O_2}$, but that's only because we have a huge amount of plant life (primarily algae) constantly producing it. If you removed all life from the Earth, the oxygen in the atmosphere would quickly oxidize out and you'd be left with an atmosphere primarily of nitrogen and a few smaller constituents.

What this means is that if we do see a substantial amount of oxygen on a planet, the best bet is that that oxygen was artificially produced by life. It's not ironclad evidence, but its a very strong indicator. We can search for oxygen through a few techniques that already exist. They're still being developed, but the technology is very quickly coming to fruition. Ultimately, you'd need to look at the spectrum of the planet's atmosphere. This can be achieved by either looking at the star's light as it passes through the planet's atmosphere, or else observing at numerous wavelengths and seeing how the transiting planet's radius changes (due to changing atmospheric opacity at different wavelengths).