I first read about it years ago in a book called Body Language. Here is a linky at http://www.psychmechanics.com/2015/04/body-language-steeple-gesture-of-hands.html
http://www.psychmechanics.com/2015/04/body-language-steeple-gesture-of-hands.html
Excellent, brief article. Steepling shows confidence in one’s knowledge. I think Trump using the gesture well. I particularly liked his use during his first meeting with Odunga at the WH.