How is "yang" functioning here?
It is not qualifying "ini" in some way, is it?
Yes, it is.
"yang' refers directlly to "ini", giving extra emphasis on "ini".
The same as in English, where the word "one" refers to "this" and gives it extra emphasis.
Coba kerjakan ini = Try doing this.
Coba kerjakan yang ini = Try doing this one.