What information is the other player required to share when forced to answer a question truthfully 'to the best of their ability'? I recently got into an argument over the other player not answering to the best of their ability as the flare states over a question with a specific answer.

The question in question was "What card are you playing?". Which the answer I was seeking refers to a specific card. Their response was just "An attack card", which I contend is intentionally vague, against the rules of the flare, and was a type of card as opposed to a specific card. My question was not "What type of card are you playing?". The real meat of the argument came down to the phrasing of the flares 'To the best of their ability' which In my opinion the other player was not fulfilling. They countered with claiming that they could have just held up a card without showing it to me and answered "This card" as well, which I also don't buy with the wording of the super flare.

So who is in the right here? Does one really have to ask long and redundant questions to get them to answer in the way you want? What level of vagueness is allowed here?

I'd tend to side with you on this one, but I think a good rules lawyer could win the case for the opposition. I think part of the fun of that Flare is the tension generated by ambiguous questions.

Sounds to me like the other player was not answering the question "to the best of their ability" but rather was being a jerk to the best of their ability. I hate that. You have every right to expect a reasonable answer to your question, which was perfectly clear in its meaning. Anybody who makes you spend five minutes working out your question in excruciating detail perhaps shouldn't be invited back to the table. ;-)