It depends. Basically, you can say anything that accurately describes what you are looking at.
- You are looking at the menu which says something like "Сок 200мл 50 руб".
Here you are looking only at juice, so the determiner has to apply to the juice itself: этот сок
/этого сока
.
However, since 200ml of juice is likely to be coming to you in a glass, you can use the word "стакан", just make sure the determiner is still pointing to "сок": стакан этого сока
.
Also, if the menu gives you options in the amount (200ml glass vs. 500ml jug), using "стакан" this way can specify which one you want.
- You are looking at an image of a glass of juice in the menu.
Both options from 1 apply here as well: этот сок
or стакан этого сока
. However, you could move the determiner to the word "стакан": этот стакан сока
. It is not particularly weird and will not necessarily give you away as a non-native speaker.
It does, however, invite a joke like: "Oh, this one specifically here on the page?", but chances of anyone actually saying anything like that are next to none.
- You are looking at an actual glass of juice.
Both options from 1 and 2 are perfectly fine here: этот сок
, стакан этого сока
, or этот стакан сока
.
- You are looking at a jug of juice as you order.
Again, both options from 1 apply: этот сок
or стакан этого сока
.
However, I would refrain from using the option from 2. Since you are not looking at the glass of juice, you can not use determiner to point to the word "стакан". It just sounds somewhat bizarre, as if you imply that the jug is a glass. It sounds like a slip of the tongue, so it will most likely prompt a person servicing you to confirm whether you want just a glass or an entire jug.
Finally, you can use this approach with pretty much anything that comes in any container: a glass of juice, a plate of salad, a bowl of soup, or a pack of drinks.