the dm and i have been told by a fellow player who dm's that the fact my wizard functionally has expertise in all knowledge skills is not usable during combat at all. i can't ask him if i "know" anything, during combat. can't ask if i know about a monster. know any of its vulnerabilities. commonly known weaknesses. rarely known ones. i have a +12 to all knowledges. i can't ask to know any sort of thing about combat? really? is there anything about this that isn't quite right? he's been told he shouldn't ask me to roll any knowledges at all when i see a creature. basically this player in and out of combat keeps finding reasons to say knowledge skills basically just don't have functions.
Different DMs handle Knowledge skills differently.
For instance, my idea has always been to have Knowledge checks represent merely the randomness of what you either know or don't know. Because of that, I do not require any action for a Knowledge check and I definitely allow it in the middle of combat, but on the other hand I do not allow retries or circumstance bonuses (such as
Guidance), and I generally decide whether you are entitled a Knowledge check on a specific case (vert often conditioned to having proficiency in the relevant Knowledge skill).
The RAW doesn't say this is how it should be done, but also it doesn't say that it should not be done. This is just how I have been doing for years because it's simple and I do not mind if it's not fully realistic (incidentally, I believe that overthinking the lack of realism in a RPG is a booby trap for complicating the game without reaching satisfactory results in most cases). My players are not supposed to tell me how I should run the game, but they can of course tell me whether they like it or not. However, I have learned that reasonable people will always accept the compromise of staying consistent until at least the end of an adventure, with the promise of trying out a different rule in the next. If a player cannot even accept that, I say good riddance!
As others have pointed out, I do not think you have a rules problem here, but a social problem due to another player wanting to exert leadership on the whole gaming group.
IMHO every game is first and foremost a DM's game, like a movie is first and foremost a director's movie, then it's for everybody else to contribute, but the DM/director is in charge. Again, the key is to view the
current adventure/campaign as the creative expression of the DM, but to see it as just
one adventure/campaign on a long-term hobby, where everyone else at the table can take the role of the DM for the
next adventure/campaign which will then be someone else's creative expression. If your group understands this, they won't feel the same hostility when they don't like something a DM has chosen to do in a certain way, because the underlying idea is that it won't always be the same. I do not trust players who behave as the current game must be perfect according to their personal preference, it makes me feel like they are into it as a short-term activity with no future, which is OK but in that case they should definitely not patronize those who are there long-term. My suggestion is that you bring the discussion up with your group, and promote the idea that your DM has all the rights to decide how things work, and whoever disagrees should just let it go and they can be the DM in the next adventure with their own rules.