Assuming that the pronunciation of יודעים is correct here, is this a word where ayin finally does something rather than just testing my nerves with all those random spellings? Is it a glottal stop?
The "stop" here is due to the sh'va vowel that would appear beneath the ד. Often when the word isn't carefully enunciated it sounds more like "yodim" and not "yod'im." I think I may have mentioned this to you before, but most people do not pronounce the Ayin.
I've noticed some patterns but I've never really been told any specific rules for if or when it is pronounced (except for that general rule that it's silent or it might be a glottal stop or theoretically some other weird pharyngal/glottal (?) sound). So I guess still the only thing it does is testing my nerves :)
Pretty much. My understanding is in certain populations (Yemenites is a group I've heard mentioned) they do pronounce ayin and aleph differently and traditionally that was the case. I know an Israeli- American (bummed we're no longer in touch because I'd love to ask him more on this) who despite being originally from Bulgaria, I think it was, and growing up on a kibbutz pronounces ayin and makes the argument it's pronounced differently than aleph. But he's also aware that's not the general present day pronunciation. His wife is a rabbi and does a lot of Jewish education stuff and basic Hebrew lessons and I remember them debating this sort of amongst themselves (and flowing back and forth between Hebrew and English as they do, so not the easiest to follow!) So not exactly helpful but yeah, certain subsets in Israel have different pronunciations but they're in a minority for sure. The guy I knew definitely spoke with more glottal stops than most, so I think that was how he used ayin? It was near impossible to teach which is perhaps the reason it's fallen out of use. It sounds interesting though, for sure.
Also with you that I'm regularly confusing spellings because of it as well.
If you listen to the Arabic letter ع (also called Ayin), that is what the Hebrew letter ע probably sounded like in biblical times.
Here's a clip of a Yemenite Torah recitation - it's positively gorgeous and you can somewhat hear the different pronunciation of the ע as well as differences in vowels: https://www.youtube.com/watch?v=lzOVNoSl6RM
True that it can sometimes make it hard to remember a spelling, but don't lose hope, because when you start to recognize more roots it becomes clear which letter it has to be.
The knpw what we do not = They know what we don't, so should be marked correct
I got marked wrong for leaving out the word את from הוא רואה את מי שאני שומע, so I would like to know why the word את is not required here.
Well, מִי and מַה are treated differenty. מַה can ask both for a subject and an object: מַה זֶּה what is this? and מָה אַתָּה רוֹאֶה what do you see?. But מִי can only ask for subjects: מִי אַתָּה who are you?, but needs the object marker, if asking for an object: אֶת מִי אַתָּה רוֹאֶה whom do you see? If it is used as a relative pronoun like here, the same rule applies. By the way, traditional English makes the same difference between who and whom, but has only one form for what.