with my feet = ?

That doesn't make sense. I think Professor Schollman is mistraslating something from Yiddish. The response, "How should I be, with myfeet?" might be appropriate if the question had been "How goes it?" But not in response to "How are you?"

A "How are you?" isn't usually an invitation to really tell anyone about how you really are. It's a greeting, kinda like Good day/morning/afternoon/etc. and a usual response might be, "I'm doin' fine, and you?

Here the responder is offering a complaint, and might be saying, why would you ask how I am when you know I have bad feet.

Thank you both

"Hebonics" is a (stupid) humorous attempt to define a Jewish analogue of "Ebonics", the slang dialect allegedly spoken by US black people. Jews are often stereotyped as answering a question with another question. Thus the remarks which prompted the question are a joke.

Insert the word "aching" or "sore" before "feet" to get a better idea of the (complaining) response in the joke.