I think I can answer my own question.  I've managed to get this to work using the maple-graded question type, formula answer, symbolic entry only (so that prime notation can be used).  The key seems to be that the maple-generated answer contain the operator D rather than the command diff.  For example, if you ask maple to differentiate sin(f(t)), maple will respond with cos(f(t))*diff(f(t),t).  But if you ask maple to differentiate sin(f(c*t)), then it responds with cos(f(c*t))*D(f)(c*t)*c.  You just need to substitute c=1 into the result. 

The following algorithm works for a question like "find the derivative of sin(f(t)), assuming f is differentiable":

$g=maple("sin(f(c*t))");

$ans=maple("subs(c=1,diff($g,t))");

This will enable students to enter their answer symbolically using f'(t).

I'd like to ask students chain rule questions with unspecified functions, such as "evaluate the derivative of sin((h(x))^2)" and have Mobius accept a form of the answer containing, say, h'(x).

Which question type should I use?  How should the answer algorithm be coded?  I haven't been able to find any information about symbolic derivatives in the documentation.

Hi @devon_unlockmath, I found a question in the Precalculus content pack in the starter bundle: clone the question "1.2.1d Try It #2" from "Assignment 1.2 Domain and Range" in lesson "Chapter 01 Functions":  Here's a link to the question. (Not sure if the link will work.)

In this question, the students are asked to do precisely what you want your students to do.  Edit the question and look at the grade code.  A particular library from the Maple repository is used that contains a "gradeInterval()" method.  Very easy to use.