Can you also say что ты знаешь о воре?
Yes I don't understand why they needed to create such a bizarre sentence with Вам and a neutral way to say the thing and not using normal pronoun вы.
Thir language is about to give me cancer
The most direct translation would be "What is known to you about the thief", correct? I find this to be a formal way to ask. "Я могу" versus "мне можно" kind of thing.
Yes, it is correct. Use the report button next time you will come across this task.
How does "что кому известно о...." differ in meaning and tone from "что ты знаешь..."?
Is it more demanding? More formal?
"что кому известно о ..." = "кому что известно о ..." = "who knows what about ..." (I don't know if this is correct English, maybe "Who knows something about ..." (?) ).
"что ты знаешь ..." = "what do you know ..."