It depends on context, I would say. Opere citato would mean "from the cited work" or "in the cited work" in the most relevant contexts. Opus citatum would mean "the cited work", where it could be subject or object or possibly something else. Operis citati would mean "of the cited work".
If it is a Latin text, the phrase would be expected to follow ordinary ...
Both, or either!
Opus citātum and opere citātō are different inflections of the same phrase, depending how they're used in the sentence.
If something comes from the cited work, for example, that would be ab opere citātō.
If you want a reader to look at the cited work, on the other hand, that would be vidē opus citātum.
In isolation (or in this case as an ...