Editing

The best training for copy-editing is OJT and mentoring. If possible, you should try to get work at a publishing house. For an entry level position, they usually give you some sort of test to see what aptitude you might have for the work, and then give you training.
However, increasingly the opportunities in this field are freelance, and not full-time permanent positions at publishing houses. Indeed, unless you are in a publishing center such as any or Boston, full-time positions may be almost impossible to get. This creates a chicken and egg problem: One cannot get work without having had experience, but one cannot get experience without having had work.
If you are in this bind, then any kind of certification or training you can get will be helpful. One also cannot stress enough the need to start connecting with authors, editors, and people in the publishing industry, as the vast majority of work in this field is unadvertised.
I also agree with Stephanie Fysh's suggestion about not working for free. While it might be worth the trouble to do one or two small projects at a low price for a friend or relative just to get something to put on your resume, there is a whole underclass of writers and editors who are selling themselves short by offering their services for free or at very low rates all the time. They may think that they are building a career that way, but they are only hurting themselves.
In publishing, a serious client will pay a good wage for your labor. One sees on Internet message boards people complaining about not getting paid for a job or being mistreated by a client, and it is nearly all over jobs paying less than $40. However, people who make a serious career from this work generally get paid much more than this unless it is for a very small job, and they generally get paid on time, because they are working for people who are equally as serious about publishing as they are.

The first question: Should I opt for higher studies or pursue a job after completing a course in non-linear editing? It deserves a yes for a job if you are getting a job because the actual purpose of doing a professional skill oriented course or training is to put it into use and start earning the vocational income.
If the non-linear editing, which is much in use now, is coming your way in the form of a stable job where your skills will further improve, take that as a course of higher studies as well. Getting paid for learning will be a better thing than joining another institute just because the previous place did not teach you enough to get a job.
Why: Video editing has worked for all. Those who know video editing and have the interest to work on the same field, have work. It is just about making a good connection as well as presenting good work, which gets you more work and strengthens your career.