It's a burning sensation just above my elbow joint on the back of my arm, so between my elbow and tricep (tendon possibly?). Yes, going between downward-facing dog and cobra, especially flying cobra, is exactly when it occurs - I'm going back to yoga classes soon because I'm sure my positioning is wrong when I do yoga on my own. Most often in my right elbow, which is my dominant hand.
I do occasionally do those forearm stretches to prevent typist muscle shortening - a writer friend warned me about it years ago - but I will do them more often.
Interestingly enough, I do get pain in the knuckle joint of my left little finger, which started after a bad habit I developed of using my little finger to press Control and stretching across with the same hand's forefinger to reach V and B. (I don't do that anymore!) That finger stiffens up in the cold and responds well to warm water and exercising the hand using small Chinese juggling balls. I tend to sleep on that side, and often wake myself up with my left arm completely numb. Since I read your article I've also noticed that I curl up in bed with my elbows and wrists bent and tucked into my body. I'm trying to keep my elbows more straightened now, and that certainly helped a couple of days ago when my elbow was quite sore.