"what" American Sign Language (ASL) - Lifeprint

There is a facial expression that is sometimes called a "wh-q" expression. It is the type of facial expression you should use when asking questions that have an answer other than yes or no.  Generally these questions start with the letters "wh" as do the signs WHO, WHAT, WHEN, WHERE, WHY...so you can see why we call this expression a "wh" question expression.  Expressing the concept of "WHAT" has more to do with your facial expression than your hands.  For example, if I pointed to my watch and used the "wh-q" facial expression it would mean that I'm asking you "What time is it?"  You've probably already used this sign many times in your life.

WHAT  ("huh" version) In the picture below I'm doing a general gesture for "what" 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 forward and to the sides.

Here is a variation of the sign "WHAT" that is made by extending your base hand outward. Starting near the thumb, drag the tip of your index finger downward, across your palm.  Note: I don't teach this sign in my "ASL" classes.  Instead I use the general version (above). But I'll show this other version to you so you'll be able to recognize it if you see it.  

WHAT:  (alternate version)

This sign (index dragged across the palm) is valid (and is still used by a significant number of Deaf people) but seems to be waning (becoming used less over time). Many ASL instructors consider it to be "Signed English."  However that simply isn't true. This sign has been around and used by "ASL signing Deaf" since at least 1916 since it appears in "The sign language: a manual of signs: being a descriptive vocabulary of signs used by the deaf of the United States and Canada" by J. Schuyler Long & Ferdinand A. Moeller. Imagine yourself asking an older person (perhaps deaf from old age) what time it is.  After he / she /they said "Huh? Speak up!"  You'd scrunch up your eyebrows and point to your watch while saying "What time is it?"  The person would most likely understand your body language and would tell you the time. Student: Why don't you recommend the alternate version of "what?" Dr. Bill:  It is important to instead learn to create the meaning of "what" by combining your facial expressions with your signs. Using a facial expression and a sign simultaneously (as in what-TIME?) rather than consecutively using two signs (as in WHAT TIME?) is more efficient (it is faster and takes less effort).  

Optional Reading:  Advanced discussion about the concept "what." Also see:  "HUH?"

Reference: The Sign Language. A Manual of Signs. Being a descriptive vocabulary of signs used by the Deaf in the United States and Canada. (1910). 55(3), 286--286. Conference of Superintendents and Principals of American Schools for the Deaf. https://babel.hathitrust.org/cgi/pt?id=mdp.39015004404482&view=1up&seq=7  

Notes:

The sign WHAT-DO (or sometimes referred to as DO-DO) has developed another meaning when paired with context and a neutral (or at least "not" WH-Q (furrowed brows) facial expression). In other words if you do the palm-up G-hand and change it to a closed-G-hand it can mean "what" as a non-interrogative pronoun. I like your observation regarding one handed usage. I'd be cautious about applying too many "rules" to an emerging sign but yes, I lean in the direction of the non-interrogative "WHAT" being done with one hand rather than two. Of course that doesn't mean everyone will articulate (pronounce) it that way. Then if you "do" add a WH-question expression the sign tends to mean "What?" as a general question and not as an exclamation. And thus we see the evolution of that particular sign move from spelling "what" to lexicalization paired with facial expression to create an "interjection" (a word that stands alone to express a sudden, strong emotion—such as shock, disbelief, or incredulity—rather than to ask for information. Then further evolved to be able to mean WHAT as a non-interrogative pronoun (with a neutral facial expression) or an interrogative pronoun with a WH-Q (furrowed brows) expression, or even a rhetorical question (with raised eyebrows)!