There are a couple of difference idiomatic choices depending on what subtext you wish to convey.
Here's a selection you can choose from: If you want to describe someone with implied criticism in a single word: John is work-shy .
John is indolent .
( not particularly common)
John is a do-nothing .
( not particularly common).
John is very apathetic towards work.
Or using an idiom:
John is somewhat of a nine-to-fiver .
John does enough to get by at work.
John does the bare minimum in his job.
John isn't living up to his own potential at work.
John is just scraping by at work.
John is not pulling his weight in his job.
The following may also apply: John is very unmotivated in his work.
John has no passion for his work.
John is fairly indifferent towards his work.
John is very lazy .
On the other hand, you might want to give John's lifestyle a positive spin: John has a good work life-balance .
ell.stackexchange.com/users/307/Matt
For what it's worth, I think slacker is, in fact, the right word for this.
You're describing someone who doesn't totally fail to show up, but puts in the minimum effort.
Putting in the minimum effort is slacking.
If you wanted to describe this in a more "politically correct" way, you might say the person is not very industrious .
ell.stackexchange.com/users/2634/Andrew
A goldbrick : a person who shirks responsibility or performs duties without proper effort or care.
Originally... The term has come a long way from its roots in the nineteenth century; along the way it got progressively further and further away from gold, or indeed bricks [...]
Incompetent officers appointed from civilian life at the start of the First World War with only minimal training were likewise called gold bricks by enlisted men (in the case of second lieutenants, this was probably provoked by their rank insignia, a gold rectangle)
At some point during that War, the term was extended to refer to anybody not pulling his weight, a malingerer or loafer
ell.stackexchange.com/users/1694/Mari-Lou A
He's a clock-watcher .
Only interested in when it's time to go home.
ell.stackexchange.com/users/9469/Steve Holden
Some other words that would work:
John has a [casual, lackadaisical, negligent, disinterested, uncaring] approach to his work.
Some words that would also imply that the quality of work suffers from his approach would be slipshod, slapdash, unmeticulous, careless, and haphazard.
You can find more by consulting a thesaurus.
ell.stackexchange.com/users/1883/BobRodes
Here are a couple more: John is a malingerer.
John is a clockwatcher.
From Google: malingerer : one who feigns illness in order to escape duty or work clockwatcher : an employee who is overly strict or zealous about not working more than the required hours
ell.stackexchange.com/users/1355/Tom Au
I like "John's work is slapdash" Since this describes his work, rather than John himself, it is more subtle than some of the other examples.
ell.stackexchange.com/users/2609/Biglig
What about John is a sloven or slob .
This means Schlamper in German, which is a person who fulfills his job but the outcome is of such a poor quality.
ell.stackexchange.com/users/2670/Kai Mysliwiec
Not really a 'slacker', since if I understand right thats somebody who doesn't really do anything. More like a person who works 9 to 5 (or more like 9-4 if he can get away with it) but not a minute longer. Is totally bland when fulfilling his tasks etc. Also hes not really a 'tool' I guess, since he's 'using' his employer more the other way around.(?)  Its driving me crazy that I can't find a right word ;)
What would you call a person who does a job but doesnt really care about quality of his work?
ell.stackexchange.com
<word-request>
ell.stackexchange.com/questions/10317
ell.stackexchange.com/users/2601/Riva
One might say that he is a clock-watcher; a nine-to-fiver; doing the bare minimum; just scraping by; not pulling his weight; very unmotivated; lazy; indolent; apathetic; disinterested or indifferent. You could also use slacker. Clock-watcher, slob, indifferent, slacker and do-nothing are viable options.
Clock-watcher, slob, indifferent, slacker and do-nothing are viable options.