Yes Joona is doing 2 mini-g's for every time (which is extremely hard) and yes Joona is one of the best diaboloists out there (in my opinion). Stick with doing 1 mini-g before going for 2 like he does.
I learnt it by learning single wrapped mini-g's first and getting them near perfect, next as soon as the stick swings under the diabolo to make a wrap let go (you could practice throwing a little bit too, but it varys) the wrap should form and rotate up to you where you would catch the stick first with one hand and then the string with the second hand. After this tug upwards on the string slightly and repeat the process.
It sounds confusing and I would make a video tutorial for you (and anyone else looking for help) but i am out of string
You could try digging up some old threads, I also remember seeing a very helpful tutorial which got me started on JTV.
Hope that helps!
-Alex
