Can I ask them in both places?
For that matter, would this question be better suited here?
Actually, when trying to explain the difference between ELL and EL&U, I have said a number of times that it often is not the question that decides where it should be asked, but the expected answer(s).
It may very well be possible to ask a same or similar question here that has been asked on ELL, as long as it is very clear you are not looking for the same answers.
For example, if I am puzzled about the use and meaning of the subjunctive in modern English, I can ask that on ELL and get some clear answers as to when I should use it and how to form it.
I could very well ask about the same thing on EL&U if I am interested in how the subjunctive seems to have largely disappeared nowadays, or why certain grammarians seem to put a lot more emphasis on its importance and use than others.
Although it would be more or less the same question, my wording would definitely have to make it clear what kind of answer I am looking for: do I simply want to understand some text that I encountered, or am I interested in the phenomenon and it current place in modern English (and maybe how it got to that position)?
As for your specific question, I would think that you could ask it at Academia if you are indeed wondering about the style(s) of English used there. If you are more interested in what influences exact English usage in places where English is used as a lingua franca, ELU may be a better place to ask.
If you have problems understanding the use of certain expressions or grammatical construction in that lingua franca, ELL seems to be the place to be.
In short, I would normally not say you should cross-post your questions on different stack-exchanges. Try to find out what kind of answer you are really looking for, and chose your stack-exchange based on that. Make sure that you phrase your question appropriately to indicate the kind of answers you are looking for.
At the same time it is very well possible that you are looking for different kinds of answers on the same subject. In that case you can certainly ask your question in several places. You will probably be better off rewording your question to focus on the specific area you are interested in, though.
I agree with oerkelens that to be valid on two different sites, the same question would have to have subtle or major variations appropriate to the two sites. I believe that fits with overall SE network policy.
I also agree that your example question belongs on Academia.
However, the bulk of the answer from oerkelens concerns the distinction between ELU and ELL, and I disagree with it. An alternative – as derived from the names of the two sites – is that
Perfectly clear, right? Of course not. So, speaking as someone who learnt to speak, read and write English some 50 years ago, and has continued to use it with a fair degree of success, I say it's "simply" a matter of level of mastery of the language. Still learning? Go to ELL. Already fluent? Welcome to ELU. The only difficulty, and it is significant, is in determining exactly where this level of mastery is. But perhaps it doesn't matter: Questions in the grey area can stay where they're posted, while those clearly on the wrong side of grey can get migrated.
Of course, there are many linguists, etymologists, and extremely serious English language
enthusiasts zealots who will try their darndest, with highfalutin phraseology and much quoting of the Help or About pages, that unless we're up to their very high level of understanding then we must surely belong in ELL. And then there are those who claim to know – and so should we, of course – the difference between "everyday" English and "academic" English and that it is what separates the two sites.
So where do you post your "English" questions? You, and most of the rest of us, should continue to take the titles of the two sites at face value and post where you or we think fit. Let the huffers and puffers continue their fruitless crusades, but fear them not.