How do I choose to study a single list if I want to cram for a test?

If you only like to cram that list you can simply choose that list from your active lists and study it alone. That will only give you words from that list. you can also open up the sections inside a list and choose to study individual sections only if that is preferred. Further you can click on the settings icon on the study page and from there choose to study e.g. only writing parts or reading etc.

How do I do this in the iOS app?

Currently you can't do that on the IOS app. You need to do that on the web version. It will come as a feature in coming releases of the IOS app. I think that they choose to wait with this to get the app out for all waiting customers. This and many more features will come with future releases.

I am also eager for such function
it is the main way I study
List by List
That is why so far I have so not used the app
Karim

Truly an epic fail that I can't study specific lists on the app, please update! The app is marvelous but this is a feature that just can't be missing.