Get some food dye and pour it down sink, it should leave a trace if the leak is from a waste pipe

That depends on the diagnosis.
My first step before calling a plumber would be to hire a moisture meter, I think Kennards have them, and see if you can identify…

It sounds like you've got a tricky situation on your hands with that kitchen leak. Given the age of your place, it's not uncommon for pipes to act up. Since…