Any way to do this on the iOS app ?

I wonder this aswell

Not yet. It's something we have planned for a later update.

I WILL ONLY BE ABLE TO USE THE iOS APP IN A EFFICIENT WAY FOR ME ONCE I WILL BE ABLE TO USE SKRITTER SUB LIST BY SUBLIST LIKE IN THE INTERNET VERSION

I was the whole summer off line, still with my iPad since so many things can be done also off line, reading books, comics, writing, taking photos, films and I had hoped keeping on tracks with my 汉字
May be it was said somewhere that it was not going to be a chinese writing summer, it's a shame, but the break was also an opportunity to feel the benefits of a break
One of such benefits would be to realize that out of the about 1000 Hanzi I had thought to have mastered in June, I guess that, back now in September Beijing in an online computer environment and in study mode, I guess then that I am still able to write a few hundreds max of the max. Boooh.
It's not bad after all, last year I knew zero Hanzi.
Part of the reason I was unable to work my Hanzi on my IPAD, and obviously it is only part of it, was my way of practicing sublist by sublist.
All my lists relate to my classes and I had classified my hanzi by group of twenty to forty all linked to a specific text. IPAD SKritter only offered me the possibility to work the 1000 all together reminding me that I have 4000 words still to cover.

Now I am back in Beijing, back on my computer, the App is designed for somebody else. It is the shame because the look and feel and the usage are awesome.
Much ado about nothing.

Take care and keep the good work to the developing team

At the risk of repeating a recent thread you could use a workaround such as temporarily banning words if you are cramming for a test. Basically ban everything and then only unban what you want to study. Not perfect but it should work.