A single word for "to paint and/or draw"?

Although somewhat generic, create is a word you could use. You will have to rephrase the sentence into:

The artist created a picture of a horse.

Perhaps...to illustrate?

"The artist illustrated a horse."

There is no single word that can directly replace paint/draw in a sentence. Painting and drawing are two distinct activities. In fact, artists who work in 2D do not only paint or draw. They make prints, do collages and much more. (I say this as someone who was once an artist.) Given your example, some options might be:

• Did you work in the studio today?
• Did you do any art today?

If the artist in question only paints or draws on a regular basis, then nothing beats

• Did you paint or draw today?

Another option:

• Are you still working on that piece?

How about to render?

e.g.

To render in ink

"He rendered the portrait in watercolor"

Very informally, I have seen people use the term "art" as a verb. I have never seen it used outside of art gallery websites such as Deviantart.com, but on such sites, among artists, it is a pretty common term. It is almost always used to describe the self and is completely intransitive.

Tenses

• Art (I'm going to art)
• Arting (I am arting *Most common)
• Arted (I arted. *Least common form)

Did you work on any 2D art today?

I'm not sure if you would use that sentence but that is what I would use.

You could just use the word 'draw':

Have you drawn anything today?

It's unreasonable to assume that an artist would take your question literally and leave it there.

Imagine you asked the above question, and the artist answered 'no' because he had only painted that day, instead of drawn, and then said nothing else. You would have to be pretty pedantic to give an answer like that, given the context.

It's far more likely that the artist would reply something along the lines of this, instead:

'No, but I did do a painting [...]'

Certainly, that's the simplest way to ask the question concisely (assuming that most artists aren't pedantic or prickly about word choice).

It's a bit of an obscure word but "limn" means to draw, paint, or depict with words.