Domestication of aliens is a process of finding complex life forms that are unintellegent. They could be found in subsurface oceans of frozen worlds, or on an earth like world. Before domestication, we would have to learn their behaviors to see if it is possible.
However, troubles are numerous. Back when early humans settled different places on Earth, they domesticated animals. But aliens may be much different and difficult. They might be harmful life forms. If it is already domesticated by an extraterrestrial intellegence, a conflict will occur. Using extraterrestrial life forms as a food source could be much worse.