Does graduating with a Journalism degree in Turkey (in English), enable employment in the UK?

Not sure what you mean by 'enable employment'. Are you a British (or, for the time being, other EU) citizen, or do you otherwise have the right to live and work in the UK? If not, then getting a degree in journalism from *anywhere* won't get you a work permit, if that's what you're asking.

Or are you British citizen (etc.) and trying to ask whether a degree in journalism from a Turkish university would be acceptable to an employer back in the UK? In which case, probably. Assuming you go to a decent university (the likes of Bilkent, METU, Bosphorus, Istanbul) then your degree will be perfectly valid and recognised the world over. And journalism is one of those jobs where you're not paid for the degree you have, you're paid for the job you do, and if you're hard-working and reasonably intelligent etc. you can do a great job with a Turkish degree just as well as a British or any other; whereas if you're a lazy useless layabout then even if you managed to get your degree from a good British university (not that you would, seeing as you're a lazy useless layabout, but bear with me...) you would be unlikely to get a job in the UK or anywhere else for that matter. In short, it depends far more on you, than on the degree you have or where you have it from.

No - there are no work visas for journalists in the UK, so it would be irrelevant where you got your degree, as the subject doesn't qualify.

If you were studying a STEM subject, you'd have more of an option.