Actually, what you posted means: What in life we do, resounds eternally, not in eternity. The '-e' ending in aeternus modifies it into an adverb. No biggie here, just that if you want a precisely literal translation:
Quod in vita facimus, in aeternitate sonat
Sonat here has a special usage:
sono, sonare, sonavi, sonatus V (1st) 1 1 [DXXAO]
|echo/resound; be heard, sound; be spoken of (as); celebrate in speech;
In aeternum is a prepositional phrase serving as an adverb. It literally means "into the eternal [possibly insert noun here]". In perpetuum is "into the perpetual [possibly insert noun here]" etc. Latin tends to use such phrases to refer to those ideas (my CLC book used in perpetuum as its only form of "forever", which is where I get the idea that it was common idiom)
Aeterne is an actual adverb, which Latin is not quite as fond of as English is. It would most accurately be translated as "eternally".
There seems to be some confusion about what's going on here. Are we trying to translate "Quis Nos Operor In Vita, Refero In Infinitio" into English? If so, we should really be in the Latin-to-English section.
But this, as it stands, seems to me to be very poor Latin. Operor ("to busy oneself" or "to perform religious rites") is a first-person singular form. So nos ("we") cannot be its subject. Furthermore, it is strictly transitive-- so nos cannot be its object. So apart from the in vita ("in life") I can't make any sense out of the part before the comma. "Refero in infinitio could mean "I recall in infinity"-- if there were a word, infinitium, meaning "infinity", which as far as I know there is not. The nominative in question might be infnitio (in which case we might have in infinitione, or in infinionem), or infinitum (in infinito, or in infinitum). Let us suppose that in infinitio is an error for in infinito, and move on. One might expect a future tense here (referam) but that's a minor point. What will "I" recall? Quis is usually an interrogative, but it can be a relative meaning "anything that" or "anyone who". But quis can not be the object of operor, which, as I have pointed out, is intransitive-- and even if that were not the case, quis is a masculine /feminine nominative.
So we have what amounts to gibberish. But hold on, perhaps all is not lost. Is this something that someone heard in a movie? Perhaps they did not hear part of it correctly. What is the minimal emendation we might make to come up with a meaningful sentence? Maybe