Trouble understanding limiter circuit with diodes
There are only two non-trivial nodes : it's reasonable to assume Vo is one of them.

One approach is to assume each in turn is Vo and solve for that.

If both yield the same answer, ... good.

If they yield different answers, you can either report both, or pick one and clarify your assumption as part of the answer.

EDIT following comments...


  Hmm, I can't seem to get an answer that matches any of the three intervals stated in the problem. Depending on what node I interpret as Vo, I get these two intervals: Either Vo ∈ {-3,5V ; 0,6V} or Vo ∈{-2,9V ; 1,2V}.


I don't see anything wrong in your result. 

One of those ranges is a subset of (i.e. contained entirely within) one of the given intervals. 

I would answer on that basis, noting the ambiguities (and your choice of Vo) and discrepancies as part of the answer.

Funnily enough, this is a very common real world situation : ambiguous or incomplete specification and unchecked calculations, (here, possibly inherited from a different question with different resistor values, not re-checked). Learning an honest and diligent way of dealing with such a situation is a necessary life skill in engineering; not much taught in coursework.