Does anyone know of any course called Mathematical Knowledge for Teaching? Where is this course taught? If it's not a course, is there any workshop about this? Or possible a book? It's not knowing how to do math but how to teach math (focus on conceptual understanding and problem solving rather than merely procedural skills) especially in elementary/middle school.
(Perhaps this should be a comment, but it's pretty much an answer.)
Mathematical Knowledge for Teaching (MKT) is based on the more general term Pedagogical Content Knowledge (PCK) due to Lee Shulman. For MKT, see the work of DL Ball. Link.
Deborah Ball is currently at the University of Michigan; you can find courses and related research projects on MKT there. For example, see this section of her site.
Here is an image to help summarize the MKT model (see here for more):
Benjamin gave the appropriate answer about what is MKT (and the famous diagram known to my friends as "the egg").
I'm hoping to address the part of your question in which you are looking for a course that might help you explore the idea of "how to teach math (focus on conceptual understanding and problem solving rather than merely procedural skills)." This sort of view of math falls very much within Jo Boaler's research. And you're lucky, because she has a free online course How To Learn Math running in a couple of weeks, open for registration now.
The summer version of the course is for educators, and the school year version is for anyone wanting to learn more about their own math learning.
To be clear, this is not a course about MKT. It's a course that addresses math teaching and learning from someone who values a problem solving approach.
Here's a video with Prof. Boaler talking a little bit about her approach.