If this is something that has only arisen 'due to the current situation', I wonder if it is symptomatic of an "XY problem": what underlies all of these requests? It may be that your students are just chancing their luck to get an easier ride, but it may also be that they are facing legitimate difficulties in studying. Investigating this may help you address their concerns and ensure fairer results for everyone.

"I'm sorry, I cannot do that Dave." But seriously, simply explain why you will not go beyond providing some sample exams (namely, the point is not to merely pass the exam, but make sure that they actually understand the material). Kindly, but firmly.

One thing to keep in mind is that there is no downside, and a large possible upside, for students to ask these questions. If you say no, no harm done, but if you say yes and give them what they want, it is easier to study for the exam - why wouldn't they ask these questions?

@StephenS makes a very good point. I doubt that there is anything you can tell the students that will convince them that they shouldn't make such requests in the first place. Just politely tell them "no".

"If we're discussing it in class, there is a chance that it will be on an exam. While you be tested on a subset of the material, that subset can change, and you are expected to understand all material presented"

Is this trend similar to your other semesters, or significantly worse at this time? I'll say in my limited observation the interactions in my now-distance courses are pretty similar to any normal semester (moreso than I expected, actually). Were you plagued with this begging before the distance learning started?

Demonstrate and tell them, "" I'll make a note of your request on paper and will give it thought later, not now. that's all" next topic. later you can say Yes/No. firmly having given it a minute of thought. Best to discuss with colleagues to have a firm idea of what goes and what doesn't and firmly state your policies to students. have a confident resolve of being the director of discussion on extra curricular topics.

I prefer the "Zen" method- a silent blow across the head and shoulders.

Why don't you give them more exam papers with solutions? If the answer is that you want to re-use questions, then just be honest and say no. Or if the course has changed since 3-years ago then that would also be a reason.

@StephenS there might be a downside: most of these questions show a desire to do the bare minimum to pass the exam/get some grade, rather than interest in the material. This could be considered in the future, e.g. when writing letters of recommendation. Which is why it's good to ask how to educate students about this, they might not realise it.

I think before answering these questions an important extra question that needs to be asked is,"Are you teaching the same as you did in all other semesters?" i.e. Have you provided online realtime lectures, where students can ask questions as they would normally? Have they had the same access to office hours they would have normally through online methods? Have they had the same number of TA lessons as they would normally? If the answer to any of these is no, "Have you reconsidered the exams and do they know it?"

The reason I'm asking is that I've seen what some professors have done given the current situation and it pretty much boiled down to, "I don't know how to use any online methods of tuition so read the books and write extra essays/homeworks/exams and I'll grade on that." In essence meaning much more work for students resulting in significantly worse teaching outcomes through no real fault of their own. If this really was sufficient we could just cut teaching staff by 80% and the students could pay 20% of their tuition fees.

It's standard practice at least in US universities to have a handout at the start of the course covering the course structure, exam format, lecture slides, extra credit, grading policy, code of conduct, prerequisites etc. etc. Doing that also means you can reply to any ther requests with a one-liner: "This is already all covered in <handout>, please refer to it". Also (and esp. viz item 4), assuming exams are remote, the only sane policy is to design the exam to be open-book and open-notes.

Also, to calm jittery nerves and people trying to study effectively in isolation, it helps for you and/or your TA to have some general review/ tutorial/ ask-me-anything sessions (not that you answer every question), and I assume you already had a midterm exam (remote?) and reviewed its solutions and grading.

If you lecture in the same manner you wrote this question there's no wonder why students want clarification. There is subject-verb disagreement in every paragraph of your question, you are receiving the requests - not experiencing them, you are a professor at a university, not "uni". Precision of language is important, especially in fields where application and understanding of theory is required.