Recall Knowledge

If a Recall Knowledge check is successfu, is it a fair question to ask the GM what the enemy's weakest save is?

I don't think you get to "request" anything. Ever.

You didn't in PF1 either, but a lot of people played it that way.

If you succeed in the check the GM decides information give you. I don't even see where it explain how many pieces of information to give. A success seems to clearly give one piece, but a critical success can give...2? Maybe more.

RAW recall knowledge doesn't actually give you anything useful. So most GMs have to houserule it to give more information to make it worth using. I think that's a fair question to ask, but of course check with how your GM wants to rule things.

That a successful recall knowledge action wouldn't get you a useful piece of information is a pretty weird reading to be claiming as RAW. There's definitely no houseruling needed for recalling a piece of knowledge or a useful clue to give you a piece of knowledge or a useful clue.

Is a troll being weak to fire or a dragon having a breath weapon useful? If it's something obvious is doesn't seem useful to me.

Dragons having a breath weapon is something everyone is likely to assume. The deal with trolls and fire is a fantastic example of useful knowledge, if you have new players who don't already have metaknowledge about the tradition of DND trolls.

Asideal from that, though, there are a lot if creatures with a lot of abilities, some of which are new enough that even experienced players wouldn't consider them obvious if they haven't come across them yet. Where exactly are you getting the idea that there is a written rule that recall knowledge would only give you things you already know, or that aren't useful to know?

Page 506: "A character who successfully identifes a creature learns
one of its best-known attributes—such as a troll’s
regeneration (and the fact that it can be stopped by acid
or fre) or a manticore’s tail spikes. "

"Sometimes a character might want to follow up on a check
to Recall Knowledge, rolling another check to discover
more information. After a success, further uses of Recall
Knowledge can yield more information, but you should
adjust the diffculty to be higher for each attempt. Once a
character has attempted an incredibly hard check or failed
a check, further attempts are fruitless—the character has
recalled everything they know about the subject."

That says that you start with one of the best known bits of information, which can be new information if the creature is not something you already know about from previous experience, and that you can proceed onward to more obscure information. Even without accounting for feats like Know It All, to get more information per action, that is not a rule that Recall Knowledge gives nothing useful.

But you try a Recall Knowledge check to get information on a topic. And the player sets the topic on which they want to try Recall Knowledge.

So after identifying a creature, a player can ask further questions. The section on page 506 gives the example of the "infamous dragon’s exploits" as a topic. A player could set the topic to "weaknesses of the infamous dragon" - the GM can set that to a hard DC if it's hard to get knowledge.

Identifying the monster is only the first step. The topic for further checks can be set differently.

But I think the question of "Can you specifically request to know the creature's weakest save?" is a firm no. You don't get to request. The GM decides what information they want to tell you. Even if you ask "What are their weaknesses" they're under no obligation to tell you their weakest save.

However, a nice GM might do so.

This is why hypercognition and the related enigma bard abilities are actually useful. If you make several consecutive knowledge checks the GM does have to keep giving you stuff, eventually it'll be what you want if the GM isn't out of his depth or trying to frustrate you, which admittedly may not be as rare as we'd all hope.

For Hypercognition do you automatically successfully make six recall knowledge checks or do you just get to make six checks but still have to roll in order to succeed on each of them?

"TRUE HYPERCOGNITION
[one-action] FEAT 14
BARD
Prerequisites enigma museYour mind works at an incredible pace. You instantly use up to five Recall Knowledge actions. If you have any special abilities or free actions that would normally be triggered when you Recall Knowledge, you can’t use them for these actions."

I don't see anything to suggest automatic success. Each recall knowledge action works by default rules.