The facial expression here is what we call a "wh-q" expression. It is the type of expression you should use when asking questions that have an answer other than yes or no. (Generally these questions start with such signs as WHO, WHAT, WHEN, WHERE, WHY...so you can see why we call this expression a "wh" question expression. The sign "what" has more to do with your facial expression than your hands. For example, if I pointed to my watch and used the facial expression it would mean that I'm asking you "What time is it?"
In the picture below I'm doing a general gesture while using the WHAT facial expression.
Hold your relaxed "5" hands in front of you. Hunch your shoulders a bit. Jut your head forward a bit. Use a WH-Q (wh-question) facial expression. The hands move slightly farther forward and to the sides.
WHAT: (alternate version)
Here is an old variation of the sign "what" that is made by
extending your left hand outward. Starting near the thumb, drag the tip of your
right index finger downward, across your palm.
All material copyright © 1996 by Dr. William Vicars
Optional Reading: Advanced discussion about the concept "what."