Does the dialog make sense?

Hmmm, no, it's missing something. "Where can I find a discussion forum?" works. "What part of that is interesting?" works. "Which of these forums are the most interesting?" works.

Can you elaborate a bit on what question is meant to be asked?

I can think of a way that it makes sense.

Person A: I'm looking around at a bunch of sites.

Person B: What is interesting? [Would probably be more like "Do you see anything interesting?"]

Person A: This site called Able2Know is pretty interesting.

Interesting is an adjective, it needs to describe a noun.

"Where is interesting? " does not contain a noun.

Romance languages usually imply the person within the verb. So one can make sentences such as: "¿Donde es interesante?" (Spanish) or "Dov'è interessante?" (Italian). "Es" and "è" imply an undefined third person singular.
That would translate to: "Where is it interesting?".

Yup, an example is:

"Importante é falar corretamente"

Nice mates, you-all are perfect!