This may belong in "Against the Mainstream" because it's rather speculative, but it's still an interesting CETI problem.
Europa is heated by its other moons forcing it to have a somewhat eccentric orbit, and thus, variable Jovian tides, though this heating is not as strong as Io's. It is enough to enable its surface to be re-created very recently by geological standards, as the paucity of craters on its surface indicates.
This heating implies that there may be hot springs at the bottom of its ocean, and maybe prebiotic chemistry and even life. The primary producers would likely be methanogen-like microbes; there may be others that live off of these.
However, there may not be free oxygen, meaning that metabolism of consumed prey would be limited to fermentation, which is relatively inefficient. This may preclude the appearance of macroscopic animal life, such as tube worms and plankton-eating filter feeders.
This makes sentient life unlikely, but it is nonetheless intriguing to speculate about "Europan dolphins", as I decide to call them. Though "Europan octopuses" might be a reasonable alternative for a sentient inhabitant to be.
They would be blind, since there is almost certainly no light in Europa's ocean, but they would have well-developed hearing and would use echolocation (sonar) rather intensively. And they would also be very talkative.
Contacting them would be a serious challenge,since they would likely prefer to live in the lower depths of Europa's ocean, where the hot springs are. This means that one would have to send a submarine *very* far down. For safety's sake, it is best that they be robot subs, at least initially.
Let's imagine approaching a pod of Europan dolphins; they would not be able to see the sub's headlights, but they would hear its odd sounds and its odd sonar signature. The dolphins would look white, because there would be no adaptive value in being pigmented.
One serious communication problem is the lack of a clear "Rosetta Stone" such as pictures; however, one could create a Braille equivalent of pictures on a flat surface by putting small rocks on it or by dragging a robot arm on it if it is sediment. A Europan dolphin may still find it difficult to understand, but a Europan octopus may have more success, because it could feel the Braille picture with its tentacles.