Asking GM knowledge questions

Is it reasonable during combat when making knowledge checks against enemies to ask "what's the enemies lowest saving throw?" And what are some good questions to ask when playing a Witch trying to get information on my enemies.

Typically, a knowledge check equal to the creature's DC should tell you the creature's type and subtype information. This information includes which are good and bad saving throws for a creature of that type.

However, expect a lot of table variation when it comes to Knowledge checks. There's no RAW requirements as to what information the DM needs to give you.

It's reasonable, but it's also a question a GM will likely say no to. A better phrasing might be "Is the [creature] known to be particularly weak-willed? Or does it struggle to evade attacks and spells? Is it known for being unusually physically unfit and lacking in fortitude?" I suspect most GMs will take better to questions like that, since it sounds less meta-gamey, but a denial (or roundabout "you don't know that") is still on the table.

"Does it have a mind / Is it susceptible to enchantments" is useful if you're unsure, since there are several Witch abilities + spells that are mind-affecting.

most gms i know set the dc for the check and every 5ish you beat the dc you get 1 question and you can ask anything from saves to immunities to weaknesses and some will even just let you look in the bestiary if you get a high enough roll had that happen a couple times when i rolled over 55 on some knowledge rolls

I believe it is reasonable. Whilst some might claim it to be metagamey, the stats allow us to objectively gauge how likely a course of action will be. As you are not actually there in person, the stats are the only way to have the description make objective and comparative sense.

Eg the creature's scales are as hard as the finest shields but it moves awkwardly. You know that means the creature has a high natural ac but a low dex but are none tge wiser about how likely your sword is to hit it. Saying the above and adding it is AC20 gives you a better picture

most gms i know set the dc for the check and every 5ish you beat the dc you get 1 question

Note that by the rules it's supposed to be one bit of useful knowledge for hitting the DC and one more bit of knowledge for every 5 you beat it by. I've seen it done as you need to beat the DC by 5 to get anything useful, and that seems pretty harsh to me.

When running a scenario as part of my prep I look through it and try and second guess what critters are likely to be subjected to knowledge checks.

Then I apply various DCs to bits and bobs starting with common knowledge working my way up to rare adding 5 to the starting DC for each step.

For what is realized in each step I think about what the PC might have picked up from reading up on it or overhearing in the ubiquitous adventurer's lodge.

I think this has been glossed over in the bestiaries and would have been a fantastic addition...maybe a gap in the market for someone.

My GM usually just tells us "It's a <thing>", as long as we exceed the base DC for it, and lets us look it up. I remember failing one badly, "It's a zombie." It turned out to be a Kuborozu... Needless to say, the wisdom damage was rather a surprise.

Yes it is completely fair to ask that. However it is also completely fair for him to judge that you didn't roll high enough for the answer. It is also fair for him to mislead you by a bit as knowledge checks refer to the typical member of a race. Dam awakened ninja T-rexes. As for the phrasing that is also perfectly fine. I assume in most cases that questions directed towards the dm are out of character, particularly those about metagame information that your character somehow knows about. There's no reason to get huffy with someone who is asking out of character about BaB instead of skill at arms. As a witch "What do I know about their saves?" and "What do I know about their immunities and resistances?" are pretty much all you need. After that be nice and ask about ac for the fighters

Also, stats can be empirically determined for non-unique individuals in-setting, so it's not that metagame to ask for them.

Usually, early on in the campaign, I will establish with the GM the kind of information I'm interested in for creatures. I phrase it such that these are the things that the character studies and researched about when learning about new creatures from books, other adventurers, etc.

For example, I was playing an Intimidation Inquisitor. His entire background was about being the scariest dude in the yard. The first thing he wanted to know about any creature he tried to identify is whether or not it was possible to scare it, because that's the first thing he'd want to know. Anything that came after that was just odds-and-ends he picked up while trying to find out that first thing.