I would like to post my question at both English.Stackexchange.com and Linguistics.Stackexchange.com. I think that the question, How do I write certain IPA sounds using Gregg Shorthand? (reposted: https://linguistics.stackexchange.com/questions/2752/help-me-convert-the-english-phonetic-alphabet-to-gregg-shorthand#comment7397_2752), is more suitable for English.Stackexchange.com because Gregg Shorthand is for English; however, the people at Linguistics.Stackexchange.com would probably be better equipped to answer the question. So, can I fork it. If not, one of the higher-up users at English.Stackexchange.com has recommended that I migrate the question. How can I migrate it?
I'm one of the mods at Linguistics. You question has been migrated yesterday (after this question was asked) and you self-deleted it.
Anyway, I'll repeat things I've already said in the comments there to clarify some points.
[...] is more suitable for English.Stackexchange.com because Gregg Shorthand is for English
This is not a valid reason. We have many questions on Linguistics that treat about English only. The only factor that could distinguish a valid question here or there is: is it about Linguistics or about Grammar and Usage? I think your question is more about the first point than the second one. Actually, it's all about the first one and nothing about the second one.
So, can I fork it
Well, in general you should ask on the site whose expertise is closer to the type of answer you want to get. Note that, if you ever choose the wrong site, you can flag your own question for migration and it's a common practice. If you want to avoid that, you might try asking on Meta/Chat first like "Is my question OK for this site?", that's a perfectly good question for Meta. And actually it's a typical Meta question.
In any case, generally you can adapt the same question to fit the site's expertise and gain answers that would be relevant for that site. But in your case I don't see how that could apply. If you have a way to do it, propose it and the EL&U community will evaluate that.
When you cross-post the same question on different sites, you should make it suit for the site where the question is being asked; in none of the cases you should ask the question exactly in the same way you are asking it in another site. In the specific, you should ask about the grammar/usage aspect on EL&U, and ask about the linguistic aspect on Linguistics.
As for the question you are referring to, the question probably suits better Linguistics, provided you can make it a good question. So far, the question has been closed as not a real question, which means it is probably too broad to get an answer.
Migrating a question is possible if you flag it for moderation attention, and you explain you want it migrated on another site.
Bear in mind that not good questions are not migrated, which means that subjective, and not constructive questions are not migrated, as they would be not constructive in any Stack Exchange. Also, generally moderators ask to the moderators of the other site if they want the question, and the migration could not happen simply because they have already very similar questions. Then, old questions are not migrated, as they would not get more attention in the receiving site; if you asked a question 3 months ago, it is rather difficult it gets migrated.