"He is very precise in his job."
Translation:Il est très précis dans son travail.
No clear rule, only more things to learn! It is very rare that a preposition can be changed without at least a change in meaning.
"Il est très précis à son travail" would mean something slightly different: it would mean that when he is at his office, everything he does (including arriving on time in the morning) is done precisely.
So, with "in his job" you are stuck with "précis dans son emploi/boulot", which is a technical aspect (as a watch-maker, for instance).
A number of more or less close synonyms can be found for "precise". Duolingo teaches you "précis" because it it the direct translation. In real life, you can hear other adjectives, like minutieux, méticuleux or rigoureux to qualify someone "precise". But Duolingo cannot list all of them.