Translation:As you know, mom knows how to do everything.
Yes, умать is always about doing (and almost always used with verbs), whereas знать is about knowledge.
"Mom knows everything" to me is about knowledge, and so would have to be знать. "Mom knows how to do everything" is akin to "Mom can do anything" and so needs to be умать.
I am confused about the use of 'kak'. I don't see its purpose. There was a good explanation on duolingo, but I did not see how it added extra information to the sentence that someone would not have understood.
For example, they talked about the dancer. I felt like if they left out 'kak', I still could understand the sentence. Am I wrong?