Hi guys, quick question regarding a rule not directly game play related.

So we had a situation in a game earlier today where I asked my opponent the trigger cost of one of their cards ability. In this case, it was Junebug. Let me clarify. My opponent had a card advanced twice, and I thought that it could be Junebug. But I was unsure as to the cost to trigger it. So I asked, but my opponent didn't want to tell me. At this point, I didn't know if it was Junebug or not, I was merely positing.

My question is, is my opponent obliged to tell me, are they allowed to refuse, or is it completely up to them? Is each player supposed to have encyclopedic knowledge of all the cards in the game, or am I allowed to find out? What would happen in this case in a tournament?

Thanks for any advice.