So...I have an interesting situation that came up last night.
Identifying a creature is the 5/10/15 + CR which gives you their type and subtype (if applicable), perhaps their name, and a certain number of additional questions based on how much you beat the DC by. My question is actually not for that.
Let's say that players know that they are going to be facing X type/subtype (they've been told by an NPC). What kind of roll, if any, is needed for a character to know if that type/subtype is, in general, susceptible to their primary class ability.
For specifics, the situation in question involved a witch who was told they would be facing devils. She was wondering if her Evil Eye hex would work against them. Does she know that, normally, devils are susceptible to her hex, or is there a roll involved? She's arguing that since it's her main hex (and right now her only one), that she is versed in its use and her character knows that some creatures are immune to it and other aren't.
Note I'm not asking about specific creatures that might be different from the norm, I'm just talking about type/subtype-based questions.
-Michael